High-Sensitivity MAX30102 Heart Rate Sensor Pulse Detection Blood Oxygen Concentration Test Module Ultra-Low Power Compatible for Arduino STM32

Datasheet is available on the DIYMall Seller Site. It works and is incredibly small. The Vin pin takes 5v or 3.3v, and it works on your FINGER or WRIST. Testing it against a $4000 startups watch, I'll update in a month after the study concludes. Its worth it! Make sure to use the MAX3010X Lib if your using it with Arduino, There are 2 other similar libraries (MAX30100) that will not work with this despite being for Pulse oxy meters.

This sensor works as expected with nRF5 microcontrollers, but the various libraries and measurement algorithms I have ran across do a poor job at accurately measuring heart rate. Precision pulse timing is handled internally (VERY useful in certain applications, as compared to the analog "Pulse Sensor" models) with internal pullups for I2C at whatever VCC voltage you feed the sensor module. Did the trick for my application (wrist-mounted heart rate sensor for decorative lighting) but would be wary of using this for situations where precision is needed without working to develop a better beat detection algorithm first.