Research-grade JavaScript code for estimating users' current heart rate on a smartphone from within the browser, using accelerometer sensors. Acceleration is obtained using `DeviceMotionEvent', the signal is smoothed using Savitzky-Golay filtering on two timescales (slow y-movement - breathing and fast y-movement - heart beat), slow breathing movements are subtracted, and peaks are counted in the remaining signal to obtain an approximate beat frequency.
A live demo can be found at tiny.cc/browserbpm. (note - this will only work on a smartphone and with a browser supporting `DeviceMotionEvent'). Tested on Chrome for mobile.
Note: this is an unrefined proof of concept and work in progress (accuracy is not verified, parameters are not tuned, speed not optimized, code is not cleaned up etc.).