back in 1988, when i was 20, i bought a heart rate monitoring watch by Casio for ~$250. You wear a strap with electrodes on your chest, and it transmits to the watch your heart beat. I wore it 24/7, for like 5 years. I was to become a borg. But today, no thanks.
of heart beating watchers, the old tech do by measuring skin resistance. i.e. a belt with electrodes around your chest, emit radio signal.
i don't remember the Model. If anyone knows, please let me know.
fitbit heart beat
another ad tile on win 10 startup menu is “fitbit coach”. The thing it tries to sell is this
this thing, monitors your heart rate, steps, sleep pattern. it's designed for yuppies who think wearing it can kick you into action.
Modern ones, do by optics. It shines light into your skin and look at the blood vessel pattern.
on the topic of heart beat, one must now read: “The Tell-Tale Heart” By Edgar Allan Poe