The heart rate is calculated manually by counting 20 heartbeats and using the timer.

Here are a couple (and I recall one other project but I can't remember the name of it right now) open source alternatives for those who aren't trying to fw a proprietary app/closed source system.

https://github.com/joeycastillo/Sensor-Watch https://github.com/PegorK/F91_Kepler

This casio model offers a step counter and pairs with the phone. You can for instance find your phone with the watch https://www.casio.com/us/watches/casio/product.ABL-100WE-1A/

Could i make this beep/vibrate on iPhone: - incoming call? - incoming sms/Signal msg? - calendar notification?

looks suspiciously similar to Sensorwatch. I hope they did not use the code without crediting the original author

sensorwatch.net ?