It’s not very accurate. Maybe because of the camera fidelity. It was about 10bpm lower than actual for me. Seems to operate off of subtle motions caused by pulse. It was even worse at detecting breathing.
Yeah, I couldn't be bothered getting my accurate chest strap out, but my watch (which is generally very close to the strap) was anywhere from 10-20 off what it was reporting. This is sitting down, 30min after a run.
It showed my BPM at nearly half of what it really was