diff --git a/docs/tracking.md b/docs/tracking.md
index 9347949..1bb7dfe 100644
--- a/docs/tracking.md
+++ b/docs/tracking.md
@@ -138,6 +138,115 @@ The optional CSV contains only `unix_seconds,bpm`. It is created privately
 path you specify. Nothing is logged by default, and heart-rate values are not
 printed to the terminal. Delete your session file when you no longer need it.
 
+### Checking heart rate against a reference
+
+`scripts/heart-check.py` runs on your computer. `listen` shows our OSC
+readings live as they arrive, so you can watch them next to another device:
+
+```sh
+python3 scripts/heart-check.py listen --port 9000 --out ours.csv
+```
+
+Point the Frame at it with `--osc <your computer's IP> 9000`. `compare` lines
+up two recordings by time and reports the mean difference, bias, the share
+within ±5 BPM and the delay between them. It passes when the mean difference
+is at most 5 BPM, at least 80% of reference readings are matched and nothing
+was shown while the sensor reported lost skin contact:
+
+```sh
+python3 scripts/heart-check.py compare ours.csv reference.csv
+python3 scripts/heart-check.py compare ours.csv ~/Downloads/export.zip
+```
+
+The reference can be a CSV (`time,bpm[,flags]`, time in unix seconds or ISO
+8601) or an Apple Health export (`export.zip` or `export.xml`). Only heart-rate
+records within the recording's time range are read. Everything stays on your
+computer.
+
+`scripts/heart-test-strap.swift` turns a Mac into a synthetic strap. It
+advertises the standard Heart Rate Service and sends a fixed, known sequence
+(8-bit and 16-bit values and a skin-contact loss), printing each sent value, so
+`compare` can check that the Frame shows exactly what was sent. It needs
+Bluetooth permission for the process that runs it. **Untested on 2026-09-29:**
+it compiled, but on this Mac, launched from an agent session, macOS never
+delivered a Bluetooth state and no permission prompt appeared, so it never
+advertised.
+
+## Pulse from the eye cameras (experimental)
+
+The Frame has no heart-rate sensor. **Verified 2026-09-29** (SteamOS 0.4.1,
+build `20260925.6191901`): its sensors are an ambient light/proximity sensor
+(`vcnl4000`), a hall sensor (`als31300`), two passthrough cameras
+(`arcimx616`), two tracking cameras (`og01a1b`) and two IR eye cameras
+(`og0ve10`). There is no optical heart-rate (PPG) sensor.
+
+The experiment asks whether the eye cameras can see a pulse anyway. With each
+heartbeat, the blood volume in the skin around the eye changes slightly and
+its IR reflectance changes with it. This is camera-based photoplethysmography;
+near-IR works, though the signal is weaker than in green light.
+
+```sh
+python3 scripts/tracking-on-frame.py pulse --seconds 60 --show
+```
+
+How it works:
+
+- **Capture (verified).** SteamVR ships `eyetracking --calib N`, which saves
+  both eye cameras for N seconds as 400×400 8-bit IR PNGs with a monotonic
+  timestamp per frame. A 2-second test captured 177 stereo pairs, about 90 fps.
+  SteamVR's live eye tracker, part of `steamvr.service`, gets its frames from
+  the DSP and stops its cameras when the headset is off; the capture ran
+  alongside it without errors in its log. **Untested:** whether the capture
+  and the live tracker coexist while the headset is worn and tracking.
+- **Privacy.** Each image is reduced to a 16×16 grid of patch averages as
+  soon as it is complete, then deleted. The capture directory is removed on
+  exit, even after errors. No image is kept or leaves the Frame. The estimate
+  is printed only with `--show`, and sent or saved only with `--osc` or
+  `--log`, as for the strap.
+- **Estimate.** Patch traces are averaged down to 15 Hz and turned into
+  relative change. A 2-second moving median removes drift and blinks.
+  Patches with frequent spikes (the eyeball and eyelid) are dropped, as are
+  dark or saturated ones. The 20% of patches with the clearest rhythm between
+  42 and 180 BPM are combined in the frequency domain. Output is an overall
+  estimate plus one estimate per second over 15-second windows. A result
+  counts as **clear** only when the top patches agree and the combined signal
+  stands out from the noise. Otherwise the command exits 3 and sends nothing.
+  The thresholds are provisional until checked on real wearers.
+
+**Verified on synthetic data** (unit tests): a 0.3% brightness pulse in a
+third of the patches, with noise, drift, blinks and eye movement, is
+recovered within 1.5 BPM at 58, 72 and 115 BPM; noise and blinks alone are
+not reported as a pulse. **Not yet verified:** whether a real wearer's eye
+images contain a usable pulse, and how accurate it is. That needs someone
+wearing the headset and a reference, as below.
+
+### Comparing with an Apple Watch
+
+1. On the watch, start a workout (for example **Other**) so it measures heart
+   rate every few seconds rather than occasionally.
+2. Put the Frame on, sit still and look ahead. Run:
+
+   ```sh
+   python3 scripts/tracking-on-frame.py pulse --seconds 120 --show \
+     --log /home/steamos/pulse.csv
+   ```
+
+   The per-second estimates print at the end. Compare them with what the
+   watch showed.
+3. End the workout. On the iPhone, open Health → your picture → **Export All
+   Health Data**, and AirDrop `export.zip` to the Mac.
+4. On the Mac:
+
+   ```sh
+   scp frame:pulse.csv . && ssh frame rm pulse.csv
+   python3 scripts/heart-check.py compare pulse.csv ~/Downloads/export.zip
+   ```
+
+This first version analyses after the capture ends, because the method must
+prove itself before a live panel is worth building. The Apple Watch is a
+reference, not ground truth: in workouts it is typically within a few BPM of
+a chest strap when you are still.
+
 ## SlimeVR: feasibility only
 
 SlimeVR is an independent application stack. Neither of our features installs,
diff --git a/frame/tracking/pulse.py b/frame/tracking/pulse.py
new file mode 100644
index 0000000..9af7642
--- /dev/null
+++ b/frame/tracking/pulse.py
@@ -0,0 +1,326 @@
+"""Experimental pulse estimate from the Frame's IR eye-tracking cameras.
+
+Skin brightens and darkens very slightly with each heartbeat as blood volume
+changes (photoplethysmography). The eye cameras film the skin around each eye
+under steady IR light at about 90 frames per second, so that rhythm may be
+visible in the average brightness of small patches of skin.
+
+Capture uses SteamVR's own `eyetracking --calib` mode, which writes PNG pairs
+to /tmp. Each image is reduced to a grid of patch averages the moment it is
+complete, then deleted; the capture directory is removed on exit. No image
+leaves the Frame or outlives the run. This is an experiment, not a medical
+measurement.
+"""
+import bisect
+import cmath
+import json
+import math
+import os
+from pathlib import Path
+import re
+import shutil
+import subprocess
+import time
+
+ET_DIR = Path("/opt/steamvr/tools/eyetracking")
+ET_BIN = ET_DIR / "bin/linuxarm64/eyetracking"
+ET_WEIGHTS = ET_DIR / "resources/et_dsp_20250610_03136.weights"
+GRID = 16        # 16 × 16 patches of 25 × 25 pixels on the 400 × 400 image
+RATE = 15.0      # analysis sample rate, Hz; the band of interest ends at 3 Hz
+LOW, HIGH = 42.0, 180.0  # BPM search band
+WINDOW = 15.0    # seconds per windowed estimate
+
+
+# ---------------------------------------------------------------- capture ---
+
+def grid_means(pixels, width, height, stride, channels, grid=GRID):
+    """Average of channel 0 in each of grid × grid equal patches."""
+    bw, bh = width // grid, height // grid
+    sums = [0] * (grid * grid)
+    for y in range(bh * grid):
+        start = y * stride
+        row = pixels[start:start + width * channels:channels]
+        base = (y // bh) * grid
+        for bx in range(grid):
+            sums[base + bx] += sum(row[bx * bw:(bx + 1) * bw])
+    area = bw * bh
+    return [s / area for s in sums]
+
+
+def load_grid(path):
+    import gi
+    gi.require_version("GdkPixbuf", "2.0")
+    from gi.repository import GdkPixbuf
+    image = GdkPixbuf.Pixbuf.new_from_file(str(path))
+    return grid_means(image.read_pixel_bytes().get_data(), image.get_width(), image.get_height(),
+                      image.get_rowstride(), image.get_n_channels())
+
+
+class Capture:
+    """Run SteamVR's eye-camera capture and reduce frames as they arrive."""
+    NAME = re.compile(r"^(left|right)_(\d+)\.png$")
+    # Only SteamVR's own capture directories are read and removed.
+    WRITING = re.compile(r"Writing capture to: (/tmp/etcalib_[\w-]+)")
+    PREFIX = "/tmp/etcalib_"
+
+    def __init__(self, seconds, runner=subprocess.Popen, loader=load_grid):
+        self.seconds, self.runner, self.loader = seconds, runner, loader
+        self.grids = {"left": {}, "right": {}}
+        self.directory = None
+
+    def run(self):
+        # The capture tool's output goes to a private temporary file, read back
+        # to find the capture directory and failure messages.
+        import tempfile
+        with tempfile.TemporaryFile("w+") as log:
+            process = self.runner([str(ET_BIN), "-b", "CDSP", "-w", str(ET_WEIGHTS), "--calib", str(self.seconds)],
+                                  cwd=str(ET_BIN.parent), stdout=log, stderr=subprocess.STDOUT)
+            try:
+                deadline = time.monotonic() + self.seconds + 30
+                while True:
+                    if not self.directory:
+                        log.seek(0)
+                        match = self.WRITING.search(log.read())
+                        if match:
+                            self.directory = Path(match.group(1))
+                    finished = process.poll() is not None
+                    self.reduce(final=finished)
+                    if finished:
+                        break
+                    if time.monotonic() > deadline:
+                        raise RuntimeError("eye-camera capture did not finish")
+                    time.sleep(0.02)
+                log.seek(0)
+                text = log.read()
+                if process.returncode or not self.directory:
+                    reason = "cameras unavailable" if "Failed to" in text else f"exit {process.returncode}"
+                    raise RuntimeError(f"eye-camera capture failed ({reason})")
+                return self.frames()
+            finally:
+                if process.poll() is None:
+                    process.terminate()
+                    try:
+                        process.wait(timeout=5)
+                    except subprocess.TimeoutExpired:
+                        process.kill()
+                        process.wait()
+                self.remove()
+
+    def reduce(self, final=False):
+        """Reduce and delete every complete image; an image is complete once a
+        later one of the same eye exists, or the capture has ended."""
+        if not self.directory or not self.directory.is_dir():
+            return
+        pending = {"left": [], "right": []}
+        for entry in os.scandir(self.directory):
+            match = self.NAME.match(entry.name)
+            if match:
+                pending[match.group(1)].append((int(match.group(2)), entry.path))
+        for eye, files in pending.items():
+            files.sort()
+            ready = files if final else files[:-1]
+            for index, path in ready:
+                try:
+                    self.grids[eye][index] = self.loader(path)
+                finally:
+                    os.unlink(path)
+
+    def frames(self):
+        """[(monotonic seconds, eye, grid)] joined with the capture metadata."""
+        meta = json.loads((self.directory / "meta.json").read_text())
+        frames = []
+        for pair in meta["frames"]:
+            for eye in ("left", "right"):
+                info = pair.get(eye) or {}
+                match = self.NAME.match(Path(info.get("fname", "")).name)
+                grid = self.grids[eye].get(int(match.group(2))) if match else None
+                if info.get("valid") and grid is not None:
+                    frames.append((float(info["tsMono"]), eye, grid))
+        return frames
+
+    def remove(self):
+        if self.directory and str(self.directory).startswith(self.PREFIX):
+            shutil.rmtree(self.directory, ignore_errors=True)
+
+
+# --------------------------------------------------------------- analysis ---
+
+def fft(values):
+    """In-place iterative radix-2 FFT of a list whose length is a power of 2."""
+    n = len(values)
+    a = list(values)
+    j = 0
+    for i in range(1, n):
+        bit = n >> 1
+        while j & bit:
+            j ^= bit
+            bit >>= 1
+        j |= bit
+        if i < j:
+            a[i], a[j] = a[j], a[i]
+    size = 2
+    while size <= n:
+        step = cmath.exp(-2j * math.pi / size)
+        half = size // 2
+        for start in range(0, n, size):
+            w = 1
+            for k in range(start, start + half):
+                t = w * a[k + half]
+                a[k + half] = a[k] - t
+                a[k] += t
+                w *= step
+        size *= 2
+    return a
+
+
+def resample(times, values, rate=RATE):
+    """Average samples into 1/rate bins from the first sample; empty bins are
+    filled from the previous bin."""
+    if not times:
+        return []
+    start = times[0]
+    count = int((times[-1] - start) * rate) + 1
+    sums, counts = [0.0] * count, [0] * count
+    for t, v in zip(times, values):
+        i = min(int((t - start) * rate), count - 1)
+        sums[i] += v
+        counts[i] += 1
+    out, last = [], None
+    for s, c in zip(sums, counts):
+        last = s / c if c else last
+        out.append(last)
+    first = next(v for v in out if v is not None)
+    return [first if v is None else v for v in out]
+
+
+def clean(signal, rate=RATE):
+    """Relative change with slow drift removed; None if the patch is mostly
+    blinks or eye movement. Spikes (blinks, saccades) become gaps at the
+    local level rather than clipped steps, which would add false rhythm."""
+    mean = sum(signal) / len(signal)
+    x = [v / mean - 1 for v in signal]
+    half = int(rate)  # 2-second centred moving median removes drift and blinks
+    trend = []
+    for i in range(len(x)):
+        chunk = sorted(x[max(0, i - half):i + half + 1])
+        trend.append(chunk[len(chunk) // 2])
+    residual = [v - m for v, m in zip(x, trend)]
+    mad = sorted(abs(v) for v in residual)[len(residual) // 2] or 1e-9
+    limit = 4 * 1.4826 * mad
+    spikes = sum(1 for v in residual if abs(v) > limit)
+    if spikes > 0.05 * len(residual):
+        return None
+    return [v if abs(v) <= limit else 0.0 for v in residual]
+
+
+def spectrum(signal, rate=RATE):
+    """[(bpm, power)] within the search band, Hann-windowed and zero-padded."""
+    n = len(signal)
+    size = 1
+    while size < max(n * 4, 256):
+        size *= 2
+    window = [0.5 - 0.5 * math.cos(2 * math.pi * i / (n - 1)) for i in range(n)] if n > 1 else [1.0]
+    padded = [s * w for s, w in zip(signal, window)] + [0.0] * (size - n)
+    result = fft(padded)
+    out = []
+    for k in range(size // 2):
+        bpm = k * rate / size * 60
+        if LOW <= bpm <= HIGH:
+            out.append((bpm, abs(result[k]) ** 2))
+    return out
+
+
+def peak(spec):
+    """Peak BPM with parabolic interpolation between spectral bins."""
+    i = max(range(len(spec)), key=lambda k: spec[k][1])
+    if 0 < i < len(spec) - 1:
+        a, b, c = spec[i - 1][1], spec[i][1], spec[i + 1][1]
+        denominator = a - 2 * b + c
+        offset = 0.5 * (a - c) / denominator if denominator else 0.0
+        return spec[i][0] + offset * (spec[1][0] - spec[0][0])
+    return spec[i][0]
+
+
+def snr(spec, bpm, width=4.0):
+    """Power near the pulse and its first harmonic against the rest of the band."""
+    near = sum(p for f, p in spec if abs(f - bpm) <= width or abs(f - 2 * bpm) <= width)
+    rest = sum(p for f, p in spec) - near
+    return near / rest if rest > 0 else float("inf")
+
+
+def normalised(spec):
+    total = sum(p for _, p in spec) or 1.0
+    return [p / total for _, p in spec]
+
+
+def usable(values):
+    """Patches that are neither dark nor saturated for the whole recording."""
+    mean = sum(values) / len(values)
+    return 8 <= mean <= 245
+
+
+def estimate(times, patches, rate=RATE, share=0.2, window=WINDOW):
+    """Estimate pulse from patch brightness traces.
+
+    times: monotonic seconds per frame. patches: {name: [brightness per frame]}.
+    Selects the share of usable patches with the clearest periodic signal,
+    combines their spectra and reports the overall and windowed estimates.
+    """
+    cleaned = {}
+    for name, values in patches.items():
+        if usable(values):
+            signal = clean(resample(times, values, rate), rate)
+            if signal is not None:
+                cleaned[name] = signal
+    if not cleaned or len(next(iter(cleaned.values()))) < rate * 8:
+        raise ValueError("need at least 8 seconds of usable eye-camera frames")
+    quality = []
+    for name, signal in cleaned.items():
+        spec = spectrum(signal, rate)
+        own = peak(spec)
+        quality.append((snr(spec, own), name, own, spec))
+    quality.sort(reverse=True)
+    chosen = quality[:max(4, int(len(quality) * share))]
+    combined = [sum(values) for values in zip(*(normalised(spec) for _, _, _, spec in chosen))]
+    bins = [f for f, _ in chosen[0][3]]
+    bpm = peak(list(zip(bins, combined)))
+    top = chosen[:8]
+    agree = sum(1 for _, _, own, _ in top if abs(own - bpm) <= 5) / len(top)
+    series = []
+    samples = int(window * rate)
+    length = len(next(iter(cleaned.values())))
+    for end in range(samples, length + 1, int(rate)):
+        specs = [spectrum(cleaned[name][end - samples:end], rate) for _, name, _, _ in chosen]
+        total = [sum(values) for values in zip(*(normalised(s) for s in specs))]
+        window_bins = [f for f, _ in specs[0]]
+        series.append((times[0] + end / rate, peak(list(zip(window_bins, total)))))
+    return {
+        "bpm": bpm,
+        "agreement": agree,
+        "patches": len(chosen),
+        "usable": len(cleaned),
+        "snr": snr(list(zip(bins, combined)), bpm),
+        "series": series,
+    }
+
+
+def analyse(frames):
+    """Estimate from Capture.frames(); both eyes' patches are analysed together
+    on a shared time base, each sample taken from that eye's nearest frame."""
+    times = sorted({t for t, _, _ in frames})
+    patches = {}
+    for eye in ("left", "right"):
+        eye_frames = sorted((t, grid) for t, e, grid in frames if e == eye)
+        if not eye_frames:
+            continue
+        eye_times = [t for t, _ in eye_frames]
+        nearest = [min(bisect.bisect_left(eye_times, t), len(eye_times) - 1) for t in times]
+        for k in range(len(eye_frames[0][1])):
+            patches[f"{eye}{k}"] = [eye_frames[i][1][k] for i in nearest]
+    return estimate(times, patches)
+
+
+def reliable(result):
+    """Whether the estimate is clear enough to show as a reading. Thresholds
+    are provisional until checked against a reference on a real wearer."""
+    return result["agreement"] >= 0.75 and result["snr"] >= 0.5
diff --git a/frame/tracking/tracking.py b/frame/tracking/tracking.py
index 10b8612..eaf9c0e 100644
--- a/frame/tracking/tracking.py
+++ b/frame/tracking/tracking.py
@@ -341,21 +341,64 @@ def run_heart(args, osc):
             session.close()
 
 
+def run_pulse(args, osc):
+    """Experimental: estimate pulse from the IR eye cameras (see pulse.py)."""
+    import pulse
+    if not pulse.ET_BIN.exists():
+        raise TrackingError("SteamVR's eye-tracking tool is not installed on this Frame")
+    print(f"Capturing {args.seconds} s from the eye cameras. Wear the headset and keep still.", flush=True)
+    try:
+        frames = pulse.Capture(args.seconds).run()
+    except RuntimeError as error:  # capture status only; no image data
+        raise TrackingError(str(error))
+    print(f"Captured {len(frames)} eye frames; images already deleted. Analysing...", flush=True)
+    try:
+        result = pulse.analyse(frames)
+    except ValueError as error:
+        raise TrackingError(str(error))
+    clear = pulse.reliable(result)
+    offset = time.time() - time.monotonic()  # the capture's timestamps are CLOCK_MONOTONIC
+    if args.log:
+        fd = os.open(args.log, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
+        with os.fdopen(fd, "w") as log:
+            log.write("unix_seconds,bpm\n")
+            for when, bpm in result["series"]:
+                log.write(f"{when + offset:.3f},{bpm:.1f}\n")
+    if clear:
+        osc.send(args.address, [round(result["bpm"])])
+    if args.show:
+        print(f"Estimate: {result['bpm']:.1f} BPM ({'clear' if clear else 'NOT clear'}; "
+              f"patch agreement {result['agreement']:.0%}, signal/noise {result['snr']:.2f}, "
+              f"{result['patches']} of {result['usable']} usable patches)")
+        print("Per-second estimates (15 s windows): "
+              + " ".join(str(round(bpm)) for _, bpm in result["series"]))
+    else:
+        print("A clear pulse was found." if clear else "No clear pulse was found.")
+    return 0 if clear else 3
+
+
 def main():
     parser = argparse.ArgumentParser(description=__doc__)
     commands = parser.add_subparsers(dest="command", required=True)
     gaze = commands.add_parser("gaze", help="headless OpenXR; prints counters only without --osc")
     heart = commands.add_parser("heart", help="standard BLE HRS from an explicitly selected strap")
-    for command in (gaze, heart):
+    pulse = commands.add_parser("pulse", help="experimental pulse estimate from the IR eye cameras")
+    for command in (gaze, heart, pulse):
         command.add_argument("--osc", nargs=2, metavar=("IP", "PORT"), help="explicit UDP destination; no default")
+    for command in (gaze, heart):
         command.add_argument("--seconds", type=int, default=10, help="bounded run, 1..86400 seconds (default: 10)")
+    pulse.add_argument("--seconds", type=int, default=60, help="capture length, 20..300 seconds (default: 60)")
     heart.add_argument("--device", required=True, help="strap Bluetooth address already discovered by BlueZ")
     heart.add_argument("--panel", action="store_true", help="show our panel on gamescope DISPLAY=:0")
-    heart.add_argument("--address", default="/avatar/parameters/HeartRate", help="integer BPM OSC parameter")
-    heart.add_argument("--log", help="new private CSV file; disabled by default")
+    for command in (heart, pulse):
+        command.add_argument("--address", default="/avatar/parameters/HeartRate", help="integer BPM OSC parameter")
+        command.add_argument("--log", help="new private CSV file; disabled by default")
+    pulse.add_argument("--show", action="store_true", help="print the estimate and per-second series")
     args = parser.parse_args()
     if not 1 <= args.seconds <= 86400:
         parser.error("--seconds must be 1..86400")
+    if args.command == "pulse" and not 20 <= args.seconds <= 300:
+        parser.error("pulse --seconds must be 20..300")
     def interrupted(signum, frame):
         raise KeyboardInterrupt
     signal.signal(signal.SIGTERM, interrupted)
@@ -363,12 +406,13 @@ def main():
         signal.signal(signal.SIGHUP, interrupted)
     osc = None
     try:
-        if args.command == "heart":
+        if args.command in ("heart", "pulse"):
             osc_message(args.address, [0])
-            if args.panel:
+            if getattr(args, "panel", False):
                 os.environ["DISPLAY"] = ":0"
         osc = Osc(args.osc)
-        return run_gaze(args, osc) if args.command == "gaze" else run_heart(args, osc)
+        run = {"gaze": run_gaze, "heart": run_heart, "pulse": run_pulse}[args.command]
+        return run(args, osc)
     except TrackingError as error:
         print(str(error))
         return 1
diff --git a/scripts/heart-check.py b/scripts/heart-check.py
new file mode 100644
index 0000000..1cc0fab
--- /dev/null
+++ b/scripts/heart-check.py
@@ -0,0 +1,262 @@
+#!/usr/bin/env python3
+"""Check Frame Control's heart-rate readings against a reference, on your computer.
+
+  python3 scripts/heart-check.py listen --port 9000 --out ours.csv
+  python3 scripts/heart-check.py compare ours.csv reference.csv
+  python3 scripts/heart-check.py compare ours.csv ~/Downloads/export.zip
+
+`listen` receives our integer-BPM OSC messages (send them here with
+`tracking-on-frame.py heart --osc <this computer's IP> 9000`) and shows each
+reading live, so you can watch it next to a reference such as your Apple
+Watch. `--out` also records `unix_seconds,bpm` to a new private file.
+
+`compare` lines up two recordings by time and reports how far apart they are.
+The reference can be:
+- a CSV whose first column is a time (unix seconds or ISO 8601) and whose
+  second is BPM, such as our own log, `listen --out`, or the test strap's
+  output (a third `flags` column marks skin-contact loss as "no reading");
+- an Apple Health export (`export.zip` or `export.xml`, from Health → your
+  profile → Export All Health Data). Only heart-rate records within the
+  recording's time range are read.
+
+Everything stays on this computer. Nothing is uploaded.
+"""
+import argparse
+import bisect
+import csv
+from datetime import datetime
+import io
+import os
+from pathlib import Path
+import re
+import socket
+import struct
+import sys
+import time
+import zipfile
+from xml.etree import ElementTree
+
+ADDRESS = "/avatar/parameters/HeartRate"
+
+
+def parse_osc(packet):
+    """Return (address, values) for a single OSC message with i/f arguments."""
+    def string(offset):
+        end = packet.index(b"\0", offset)
+        return packet[offset:end].decode("utf-8"), (end + 4) & ~3
+    address, offset = string(0)
+    tags, offset = string(offset)
+    if not tags.startswith(","):
+        raise ValueError("not an OSC message")
+    values = []
+    for tag in tags[1:]:
+        if tag not in "if" or offset + 4 > len(packet):
+            raise ValueError("unsupported OSC argument")
+        values.append(struct.unpack(">i" if tag == "i" else ">f", packet[offset:offset + 4])[0])
+        offset += 4
+    return address, values
+
+
+def listen(port, address, out, seconds, clock=time.time, stream=sys.stdout):
+    log = None
+    if out:
+        log = os.fdopen(os.open(out, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600), "w")
+        log.write("unix_seconds,bpm\n")
+    received = 0
+    with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as sock:
+        sock.bind(("0.0.0.0", port))
+        sock.settimeout(0.5)
+        print(f"Listening for {address} on UDP port {port}. Ctrl-C stops.", file=stream, flush=True)
+        end = clock() + seconds if seconds else None
+        try:
+            while end is None or clock() < end:
+                try:
+                    packet = sock.recv(1024)
+                except socket.timeout:
+                    continue
+                try:
+                    path, values = parse_osc(packet)
+                except (ValueError, UnicodeDecodeError):
+                    continue
+                if path != address or len(values) != 1:
+                    continue
+                now = clock()
+                bpm = int(values[0])
+                received += 1
+                print(f"{time.strftime('%H:%M:%S', time.localtime(now))}  {bpm:3d} bpm", file=stream, flush=True)
+                if log:
+                    log.write(f"{now:.3f},{bpm}\n")
+                    log.flush()
+        except KeyboardInterrupt:
+            pass
+        finally:
+            if log:
+                log.close()
+    return received
+
+
+def parse_time(text):
+    text = text.strip()
+    if re.fullmatch(r"\d+(\.\d+)?", text):
+        return float(text)
+    # Apple Health uses "2026-09-29 09:12:03 +1000".
+    text = re.sub(r" ([+-]\d{2}):?(\d{2})$", r"\1\2", text).replace("Z", "+0000")
+    for pattern in ("%Y-%m-%d %H:%M:%S%z", "%Y-%m-%dT%H:%M:%S%z", "%Y-%m-%dT%H:%M:%S.%f%z"):
+        try:
+            return datetime.strptime(text, pattern).timestamp()
+        except ValueError:
+            pass
+    raise ValueError(f"unrecognised time {text!r}")
+
+
+def read_csv(path):
+    """[(time, bpm or None)], sorted. A header row is skipped."""
+    samples = []
+    with open(path, newline="") as source:
+        for row in csv.reader(source):
+            if len(row) < 2:
+                continue
+            try:
+                when, bpm = parse_time(row[0]), int(float(row[1]))
+            except ValueError:
+                continue  # header or unparseable line
+            if len(row) > 2 and row[2].strip():
+                flags = int(row[2])
+                if flags & 4 and not flags & 2:
+                    bpm = None  # contact supported and not detected: no reading
+            samples.append((when, bpm))
+    return sorted(samples, key=lambda s: s[0])
+
+
+def read_health(path, start, end):
+    """Heart-rate records from an Apple Health export between start and end."""
+    if zipfile.is_zipfile(path):
+        archive = zipfile.ZipFile(path)
+        name = next(n for n in archive.namelist() if n.endswith("/export.xml") or n == "export.xml")
+        source = archive.open(name)
+    else:
+        source = open(path, "rb")
+    samples = []
+    with source:
+        for _, element in ElementTree.iterparse(source):
+            if element.tag == "Record" and element.get("type") == "HKQuantityTypeIdentifierHeartRate":
+                when = parse_time(element.get("startDate"))
+                if start <= when <= end:
+                    samples.append((when, round(float(element.get("value")))))
+            element.clear()
+    return sorted(samples)
+
+
+def read_any(path, start=None, end=None):
+    path = str(path)
+    if path.endswith((".zip", ".xml")):
+        return read_health(path, start, end)
+    return read_csv(path)
+
+
+def value_at(samples, when, hold):
+    """Our reading at a moment: the latest sample no older than `hold` seconds."""
+    times = [s[0] for s in samples]
+    i = bisect.bisect_right(times, when) - 1
+    if i < 0 or when - times[i] > hold:
+        return None
+    return samples[i][1]
+
+
+def compare(ours, reference, max_lag=10.0, hold=5.0):
+    """Compare our readings with the reference at each reference moment.
+
+    `lag` is the delay added to reference times before looking up ours (our
+    readings arrive after the sensor's). The best lag within ±max_lag is used.
+    """
+    real = [(t, b) for t, b in reference if b is not None]
+    if not real or not any(b is not None for _, b in ours):
+        raise ValueError("both recordings need at least one reading")
+    best = None
+    steps = int(max_lag * 4)
+    for step in range(-steps, steps + 1):
+        lag = step / 4
+        pairs = [(value_at(ours, t + lag, hold), b) for t, b in real]
+        pairs = [(o, r) for o, r in pairs if o is not None]
+        if not pairs:
+            continue
+        error = sum(abs(o - r) for o, r in pairs) / len(pairs)
+        key = (-len(pairs), error, abs(lag))
+        if best is None or key < best[0]:
+            best = (key, lag, pairs)
+    if best is None:
+        raise ValueError("the recordings do not overlap in time")
+    _, lag, pairs = best
+    differences = [o - r for o, r in pairs]
+    # While the reference says "no reading" (lost skin contact), we must not
+    # produce new readings. Count ours that arrive during such a stretch.
+    gaps = [t for t, b in reference if b is None]
+    reference_times = [t for t, _ in reference]
+    shown_in_gaps = 0
+    for t, bpm in ours:
+        i = bisect.bisect_right(reference_times, t - lag) - 1
+        if bpm is not None and i >= 0 and reference[i][1] is None:
+            shown_in_gaps += 1
+    return {
+        "reference_readings": len(real),
+        "matched": len(pairs),
+        "lag_seconds": lag,
+        "mean_abs_error": sum(abs(d) for d in differences) / len(differences),
+        "bias": sum(differences) / len(differences),
+        "max_abs_error": max(abs(d) for d in differences),
+        "within_5": sum(1 for d in differences if abs(d) <= 5) / len(differences),
+        "exact": sum(1 for d in differences if d == 0) / len(differences),
+        "no_contact_moments": len(gaps),
+        "shown_during_no_contact": shown_in_gaps,
+    }
+
+
+def report(result, tolerance, stream=sys.stdout):
+    print(f"Reference readings: {result['reference_readings']}, matched: {result['matched']}", file=stream)
+    print(f"Best alignment: ours {result['lag_seconds']:+.2f} s after the reference", file=stream)
+    print(f"Mean absolute difference: {result['mean_abs_error']:.2f} BPM "
+          f"(bias {result['bias']:+.2f}, worst {result['max_abs_error']})", file=stream)
+    print(f"Within ±5 BPM: {result['within_5']:.0%}; identical: {result['exact']:.0%}", file=stream)
+    if result["no_contact_moments"]:
+        print(f"No-contact moments: {result['no_contact_moments']}, where we showed a stale "
+              f"reading: {result['shown_during_no_contact']}", file=stream)
+    coverage = result["matched"] / result["reference_readings"]
+    passed = (result["mean_abs_error"] <= tolerance and coverage >= 0.8
+              and not result["shown_during_no_contact"])
+    print(("PASS" if passed else "FAIL") + f" (mean difference ≤ {tolerance} BPM, ≥80% of reference "
+          f"readings matched, nothing shown without contact)", file=stream)
+    return passed
+
+
+def main(argv=None):
+    parser = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+    commands = parser.add_subparsers(dest="command", required=True)
+    heard = commands.add_parser("listen", help="show and optionally record our OSC readings live")
+    heard.add_argument("--port", type=int, default=9000)
+    heard.add_argument("--address", default=ADDRESS)
+    heard.add_argument("--out", help="new private CSV file")
+    heard.add_argument("--seconds", type=float, default=0, help="stop after this long (default: until Ctrl-C)")
+    check = commands.add_parser("compare", help="compare our recording with a reference")
+    check.add_argument("ours", type=Path)
+    check.add_argument("reference", type=Path)
+    check.add_argument("--tolerance", type=float, default=5.0, help="allowed mean difference in BPM (default 5)")
+    check.add_argument("--max-lag", type=float, default=10.0, help="largest time offset to search, seconds")
+    args = parser.parse_args(argv)
+    if args.command == "listen":
+        count = listen(args.port, args.address, args.out, args.seconds)
+        print(f"Received {count} readings.")
+        return 0 if count else 3
+    ours = read_csv(args.ours)
+    if not ours:
+        parser.error("our recording has no readings")
+    reference = read_any(args.reference, ours[0][0] - 60, ours[-1][0] + 60)
+    try:
+        result = compare(ours, reference, args.max_lag)
+    except ValueError as error:
+        print(str(error))
+        return 1
+    return 0 if report(result, args.tolerance) else 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/scripts/heart-test-strap.swift b/scripts/heart-test-strap.swift
new file mode 100644
index 0000000..8441068
--- /dev/null
+++ b/scripts/heart-test-strap.swift
@@ -0,0 +1,100 @@
+// A synthetic Bluetooth heart-rate strap for testing, run on the Mac.
+//
+//   swiftc -O scripts/heart-test-strap.swift -o /tmp/heart-test-strap
+//   /tmp/heart-test-strap [seconds]      # default 60
+//
+// Advertises the standard Heart Rate Service (180d) as "FC Test Strap" and,
+// while a central is subscribed, sends one Heart Rate Measurement (2a37) per
+// second from a fixed, known sequence. Each sent value is printed to stdout as
+// `unix_seconds,bpm,flags` so scripts/heart-check.py can compare what the
+// Frame received with what was sent. Every value is synthetic; this is not a
+// sensor. macOS asks for Bluetooth permission the first time it runs.
+import CoreBluetooth
+import Foundation
+
+let hrs = CBUUID(string: "180D")
+let measurement = CBUUID(string: "2A37")
+
+/// The known sequence: an 8-bit ramp, 16-bit encodings, a skin-contact loss
+/// (which must show as no reading) and a recovery.
+func packet(_ second: Int) -> (bpm: Int, flags: UInt8) {
+    switch second % 60 {
+    case 0..<30: return (60 + second % 60 * 4, 0x06)   // 60…176, contact detected
+    case 30..<40: return (180 - (second % 60 - 30) * 3, 0x07) // 16-bit value
+    case 40..<45: return (150, 0x04)                  // contact lost
+    default: return (72 + (second % 60 - 45), 0x06)
+    }
+}
+
+final class Strap: NSObject, CBPeripheralManagerDelegate {
+    let seconds: Int
+    var manager: CBPeripheralManager!
+    var characteristic: CBMutableCharacteristic!
+    var subscribed = false
+    var sent = 0
+
+    init(seconds: Int) {
+        self.seconds = seconds
+        super.init()
+        manager = CBPeripheralManager(delegate: self, queue: nil)
+    }
+
+    func peripheralManagerDidUpdateState(_ peripheral: CBPeripheralManager) {
+        guard peripheral.state == .poweredOn else {
+            FileHandle.standardError.write("Bluetooth state \(peripheral.state.rawValue)\n".data(using: .utf8)!)
+            if peripheral.state == .unauthorized || peripheral.state == .unsupported || peripheral.state == .poweredOff {
+                FileHandle.standardError.write("Bluetooth unavailable (state \(peripheral.state.rawValue))\n".data(using: .utf8)!)
+                exit(1)
+            }
+            return
+        }
+        characteristic = CBMutableCharacteristic(type: measurement, properties: [.notify], value: nil, permissions: [])
+        let service = CBMutableService(type: hrs, primary: true)
+        service.characteristics = [characteristic]
+        peripheral.add(service)
+    }
+
+    func peripheralManager(_ peripheral: CBPeripheralManager, didAdd service: CBService, error: Error?) {
+        if let error { fail("add service: \(error.localizedDescription)") }
+        peripheral.startAdvertising([CBAdvertisementDataLocalNameKey: "FC Test Strap",
+                                     CBAdvertisementDataServiceUUIDsKey: [hrs]])
+    }
+
+    func peripheralManagerDidStartAdvertising(_ peripheral: CBPeripheralManager, error: Error?) {
+        if let error { fail("advertise: \(error.localizedDescription)") }
+        FileHandle.standardError.write("Advertising FC Test Strap\n".data(using: .utf8)!)
+        Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { _ in self.tick() }
+    }
+
+    func peripheralManager(_ peripheral: CBPeripheralManager, central: CBCentral, didSubscribeTo characteristic: CBCharacteristic) {
+        subscribed = true
+        FileHandle.standardError.write("Central subscribed\n".data(using: .utf8)!)
+    }
+
+    func peripheralManager(_ peripheral: CBPeripheralManager, central: CBCentral, didUnsubscribeFrom characteristic: CBCharacteristic) {
+        subscribed = false
+        FileHandle.standardError.write("Central unsubscribed\n".data(using: .utf8)!)
+    }
+
+    func tick() {
+        guard subscribed else { return }
+        if sent >= seconds { exit(0) }
+        let (bpm, flags) = packet(sent)
+        var bytes: [UInt8] = [flags, UInt8(bpm & 0xff)]
+        if flags & 1 != 0 { bytes.append(UInt8(bpm >> 8)) }
+        if manager.updateValue(Data(bytes), for: characteristic, onSubscribedCentrals: nil) {
+            print(String(format: "%.3f,%d,%d", Date().timeIntervalSince1970, bpm, flags))
+            fflush(stdout)
+            sent += 1
+        }
+    }
+
+    func fail(_ message: String) -> Never {
+        FileHandle.standardError.write("\(message)\n".data(using: .utf8)!)
+        exit(1)
+    }
+}
+
+let seconds = CommandLine.arguments.count > 1 ? Int(CommandLine.arguments[1]) ?? 60 : 60
+let strap = Strap(seconds: seconds)
+RunLoop.main.run()
diff --git a/scripts/tracking-on-frame.py b/scripts/tracking-on-frame.py
index 2aa39e0..e2588f9 100644
--- a/scripts/tracking-on-frame.py
+++ b/scripts/tracking-on-frame.py
@@ -5,6 +5,7 @@
   python3 scripts/tracking-on-frame.py gaze --seconds 10
   python3 scripts/tracking-on-frame.py gaze --seconds 3600 --osc 127.0.0.1 9000
   python3 scripts/tracking-on-frame.py heart --device AA:BB:CC:DD:EE:FF --panel
+  python3 scripts/tracking-on-frame.py pulse --seconds 60 --show   # experimental
 
 FRAME_ALIAS overrides the SSH alias (default: frame). Runs in the foreground;
 Ctrl-C stops the reader. No service, autostart, sudo or SteamVR settings changes.
@@ -27,13 +28,14 @@ cc -O2 -Wall -Wextra -Werror "$stage/gaze.c" \\
   -L/opt/steamvr/bin/linuxarm64 -Wl,-rpath,/opt/steamvr/bin/linuxarm64 \\
   -lopenxr_loader -o "$stage/gaze"
 chmod 700 "$stage/gaze" "$stage/tracking.py"
-mv "$stage/gaze" "$stage/tracking.py" "$base/"
+chmod 600 "$stage/pulse.py"
+mv "$stage/gaze" "$stage/tracking.py" "$stage/pulse.py" "$base/"
 echo 'Installed Frame Control tracking tools (no service started).'
 '''
 
 
 def main():
-    if len(sys.argv) < 2 or sys.argv[1] not in ("install", "gaze", "heart"):
+    if len(sys.argv) < 2 or sys.argv[1] not in ("install", "gaze", "heart", "pulse"):
         print(__doc__)
         return 2
     host = os.environ.get("FRAME_ALIAS", "frame")
@@ -45,7 +47,7 @@ def main():
         source = Path(__file__).resolve().parents[1] / "frame" / "tracking"
         with tempfile.TemporaryFile() as archive:
             with tarfile.open(fileobj=archive, mode="w") as tar:
-                for name in ("gaze.c", "tracking.py"):
+                for name in ("gaze.c", "tracking.py", "pulse.py"):
                     tar.add(source / name, arcname=name)
             archive.seek(0)
             return subprocess.call(ssh + ["bash -c " + shlex.quote(INSTALL)], stdin=archive)
diff --git a/tests/test_pulse.py b/tests/test_pulse.py
new file mode 100644
index 0000000..7b2a5b7
--- /dev/null
+++ b/tests/test_pulse.py
@@ -0,0 +1,282 @@
+"""Eye-camera pulse estimate and the heart-rate comparison tool; no headset needed."""
+import importlib.util
+import io
+import json
+import math
+import os
+from pathlib import Path
+import random
+import socket
+import struct
+import sys
+import tempfile
+import unittest
+import zipfile
+from unittest.mock import patch
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def load(name, path):
+    spec = importlib.util.spec_from_file_location(name, ROOT / path)
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+pulse = load("pulse", "frame/tracking/pulse.py")
+check = load("heart_check", "scripts/heart-check.py")
+
+
+def synthetic(bpm, pulsing, seconds=40, fps=30, patches=48, noise=0.004, seed=7):
+    """Patch brightness with a faint pulse in `pulsing` patches, plus sensor
+    noise, slow drift, blinks in some patches and eye movement in others."""
+    rng = random.Random(seed)
+    times = [i / fps for i in range(seconds * fps)]
+    values = {}
+    for k in range(patches):
+        base, amplitude, trace = 40 + k, 0.003 if k < pulsing else 0.0, []
+        for t in times:
+            v = base * (1 + amplitude * math.sin(2 * math.pi * bpm / 60 * t)
+                        + noise * rng.gauss(0, 1) + 0.02 * math.sin(0.1 * t + k))
+            if k % 8 == 7 and int(t * 10) % 47 == 0:
+                v *= 0.5   # blink
+            if k % 8 == 6 and int(t * 10) % 23 == 0:
+                v *= 1.3   # frequent eye movement
+            trace.append(v)
+        values[k] = trace
+    return times, values
+
+
+class Estimate(unittest.TestCase):
+    def test_finds_pulse(self):
+        for bpm in (58, 72, 115):
+            with self.subTest(bpm=bpm):
+                result = pulse.estimate(*synthetic(bpm, 16))
+                self.assertAlmostEqual(result["bpm"], bpm, delta=1.5)
+                self.assertTrue(pulse.reliable(result))
+                self.assertTrue(all(abs(b - bpm) <= 2 for _, b in result["series"]))
+
+    def test_noise_and_blinks_are_not_a_pulse(self):
+        result = pulse.estimate(*synthetic(72, 0))
+        self.assertFalse(pulse.reliable(result))
+
+    def test_frequent_spike_patches_are_dropped(self):
+        times, values = synthetic(72, 16)
+        result = pulse.estimate(times, values)
+        self.assertLess(result["usable"], len(values))
+
+    def test_needs_enough_frames(self):
+        with self.assertRaises(ValueError):
+            pulse.estimate(*synthetic(72, 16, seconds=5))
+        times, values = synthetic(72, 16)
+        with self.assertRaises(ValueError):
+            pulse.estimate(times, {k: [0.0] * len(times) for k in values})  # all dark
+
+    def test_series_times(self):
+        times, values = synthetic(72, 16, seconds=20)
+        series = pulse.estimate(times, values)["series"]
+        self.assertAlmostEqual(series[0][0], pulse.WINDOW, delta=0.1)
+        self.assertEqual(len(series), 20 - int(pulse.WINDOW) + 1)
+
+    def test_fft_matches_dft(self):
+        signal = [math.sin(i) + (i % 3) for i in range(16)]
+        fast = pulse.fft(signal)
+        for k in range(16):
+            slow = sum(signal[n] * complex(math.cos(2 * math.pi * k * n / 16), -math.sin(2 * math.pi * k * n / 16))
+                       for n in range(16))
+            self.assertAlmostEqual(abs(fast[k] - slow), 0, places=9)
+
+    def test_grid_means(self):
+        # 4 × 4 image in RGB with padding: left half 10, right half 30 (channel 0).
+        width, height, channels, stride = 4, 4, 3, 16
+        pixels = bytearray(stride * height)
+        for y in range(height):
+            for x in range(width):
+                pixels[y * stride + x * channels] = 10 if x < 2 else 30
+                pixels[y * stride + x * channels + 1] = 255  # other channels ignored
+        self.assertEqual(pulse.grid_means(bytes(pixels), width, height, stride, channels, grid=2),
+                         [10, 30, 10, 30])
+
+    def test_analyse_combines_both_eyes(self):
+        times, values = synthetic(80, 16, patches=16)
+        frames = []
+        for i, t in enumerate(times):
+            frames.append((t, "left", [values[k][i] for k in range(16)]))
+            frames.append((t + 0.001, "right", [values[k][i] for k in range(16)]))
+        result = pulse.analyse(frames)
+        self.assertAlmostEqual(result["bpm"], 80, delta=1.5)
+        self.assertEqual(result["usable"] % 2, 0)
+
+
+class FakeCaptureTool:
+    """Stands in for `eyetracking --calib`: writes PNG names over a few polls."""
+    def __init__(self, directory, frames=6, fail=False):
+        self.directory, self.frames, self.fail = Path(directory), frames, fail
+        self.polls = 0
+        self.returncode = None
+        self.stdout = None
+
+    def __call__(self, command, cwd, stdout, stderr):
+        self.command = command
+        self.stdout = stdout
+        if self.fail:
+            stdout.write("Failed to initialize cameras\n")
+            stdout.flush()
+            self.returncode = 1
+            return self
+        stdout.write(f"Writing capture to: {self.directory}\nCapturing images...\n")
+        stdout.flush()
+        self.directory.mkdir()
+        return self
+
+    def poll(self):
+        if self.returncode is not None:
+            return self.returncode
+        if self.polls < self.frames:
+            for eye in ("left", "right"):
+                (self.directory / f"{eye}_{self.polls}.png").write_bytes(b"png")
+            self.polls += 1
+            return None
+        meta = {"frames": [{eye: {"fname": str(self.directory / f"{eye}_{i}.png"), "frameNum": i + 10,
+                                  "tsMono": 100 + i / 90, "valid": i != 2} for eye in ("left", "right")}
+                           for i in range(self.frames)]}
+        (self.directory / "meta.json").write_text(json.dumps(meta))
+        self.returncode = 0
+        return 0
+
+    def terminate(self):
+        self.returncode = -15
+
+    def wait(self, timeout=None):
+        return self.returncode
+
+
+class CaptureLifecycle(unittest.TestCase):
+    def setUp(self):
+        self.root = Path(tempfile.mkdtemp())
+        self.directory = self.root / "etcalib_test"
+        self.loaded = []
+
+    def tearDown(self):
+        import shutil
+        shutil.rmtree(self.root, ignore_errors=True)
+
+    def loader(self, path):
+        self.loaded.append(Path(path).name)
+        self.assertTrue(Path(path).exists())
+        return [float(len(self.loaded))]
+
+    def capture(self, tool):
+        class TestCapture(pulse.Capture):
+            # A temporary directory stands in for /tmp/etcalib_*.
+            WRITING = __import__("re").compile(r"Writing capture to: (\S+)")
+            PREFIX = str(self.root)
+        capture = TestCapture(20, runner=tool, loader=self.loader)
+        with patch.object(pulse.time, "sleep", lambda s: None):
+            return capture, capture.run()
+
+    def test_reduces_deletes_and_joins_metadata(self):
+        tool = FakeCaptureTool(self.directory)
+        capture, frames = self.capture(tool)
+        self.assertEqual(sorted(self.loaded), sorted(f"{e}_{i}.png" for e in ("left", "right") for i in range(6)))
+        self.assertFalse(self.directory.exists())  # images and metadata removed
+        self.assertEqual(len(frames), 10)          # frame 2 invalid in both eyes
+        self.assertEqual(tool.command[-2:], ["--calib", "20"])
+        self.assertTrue(all(isinstance(t, float) and eye in ("left", "right") for t, eye, _ in frames))
+
+    def test_camera_failure(self):
+        tool = FakeCaptureTool(self.directory, fail=True)
+        with self.assertRaises(RuntimeError) as raised:
+            self.capture(tool)
+        self.assertIn("cameras unavailable", str(raised.exception))
+
+    def test_only_removes_capture_directories(self):
+        capture = pulse.Capture(20)
+        capture.directory = self.root
+        capture.remove()
+        self.assertTrue(self.root.exists())
+
+
+class HeartCheck(unittest.TestCase):
+    def write(self, name, text):
+        path = Path(self.enterContext(tempfile.TemporaryDirectory())) / name
+        path.write_text(text)
+        return path
+
+    def test_osc_round_trip(self):
+        tracking = load("tracking", "frame/tracking/tracking.py")
+        self.assertEqual(check.parse_osc(tracking.osc_message("/avatar/parameters/HeartRate", [72])),
+                         ("/avatar/parameters/HeartRate", [72]))
+        address, values = check.parse_osc(tracking.osc_message("/x", [1.5, -2.0]))
+        self.assertEqual((address, values), ("/x", [1.5, -2.0]))
+        with self.assertRaises(ValueError):
+            check.parse_osc(b"/x\0\0,s\0\0abc\0")
+
+    def test_listen_records_readings(self):
+        tracking = load("tracking", "frame/tracking/tracking.py")
+        with tempfile.TemporaryDirectory() as directory:
+            out = Path(directory) / "ours.csv"
+            with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as probe:
+                probe.bind(("127.0.0.1", 0))
+                port = probe.getsockname()[1]
+            import threading
+            def send():
+                import time
+                time.sleep(0.3)
+                with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as sender:
+                    sender.sendto(tracking.osc_message(check.ADDRESS, [72]), ("127.0.0.1", port))
+                    sender.sendto(tracking.osc_message("/other", [1]), ("127.0.0.1", port))
+            threading.Thread(target=send).start()
+            shown = io.StringIO()
+            count = check.listen(port, check.ADDRESS, str(out), 1.5, stream=shown)
+            self.assertEqual(count, 1)
+            self.assertIn("72 bpm", shown.getvalue())
+            self.assertEqual(out.read_text().splitlines()[1].split(",")[1], "72")
+            self.assertEqual(out.stat().st_mode & 0o777, 0o600)
+
+    def test_compare_finds_lag_and_contact_loss(self):
+        reference = [(1000.0 + i, 60 + i, 6) for i in range(40)] + [(1040.0 + i, 150, 4) for i in range(5)]
+        ours = [(1002.0 + i, 60 + i) for i in range(40)]  # 2 s late, nothing during contact loss
+        ref = self.write("ref.csv", "unix_seconds,bpm,flags\n" + "".join(f"{t},{b},{f}\n" for t, b, f in reference))
+        mine = self.write("ours.csv", "unix_seconds,bpm\n" + "".join(f"{t},{b}\n" for t, b in ours))
+        result = check.compare(check.read_csv(mine), check.read_any(ref))
+        self.assertEqual(result["lag_seconds"], 2.0)
+        self.assertEqual(result["mean_abs_error"], 0)
+        self.assertEqual(result["shown_during_no_contact"], 0)
+        self.assertTrue(check.report(result, 5, stream=io.StringIO()))
+        # A stale reading sent during contact loss fails the check.
+        stale = check.read_csv(mine) + [(1043.0, 99)]
+        result = check.compare(stale, check.read_any(ref))
+        self.assertEqual(result["shown_during_no_contact"], 1)
+        self.assertFalse(check.report(result, 5, stream=io.StringIO()))
+
+    def test_compare_against_apple_health_export(self):
+        records = "".join(
+            f'<Record type="HKQuantityTypeIdentifierHeartRate" unit="count/min" '
+            f'startDate="2026-09-29 12:00:{s:02d} +1000" endDate="2026-09-29 12:00:{s:02d} +1000" value="{70 + s % 3}"/>'
+            for s in range(0, 60, 5))
+        other = '<Record type="HKQuantityTypeIdentifierStepCount" startDate="2026-09-29 12:00:00 +1000" value="9"/>'
+        xml = f'<?xml version="1.0"?><HealthData>{other}{records}</HealthData>'
+        with tempfile.TemporaryDirectory() as directory:
+            archive = Path(directory) / "export.zip"
+            with zipfile.ZipFile(archive, "w") as z:
+                z.writestr("apple_health_export/export.xml", xml)
+            start = check.parse_time("2026-09-29 12:00:00 +1000")
+            samples = check.read_any(archive, start - 60, start + 120)
+            self.assertEqual(len(samples), 12)
+            self.assertEqual(samples[0], (start, 70))
+            ours = [(start + i + 1.0, 71) for i in range(60)]
+            result = check.compare(ours, samples)
+            self.assertLessEqual(result["mean_abs_error"], 1)
+
+    def test_time_formats(self):
+        self.assertEqual(check.parse_time("1700000000.5"), 1700000000.5)
+        self.assertEqual(check.parse_time("2023-11-14T22:13:20Z"), 1700000000)
+        self.assertEqual(check.parse_time("2023-11-15 08:13:20 +1000"), 1700000000)
+        with self.assertRaises(ValueError):
+            check.parse_time("yesterday")
+
+
+if __name__ == "__main__":
+    unittest.main()