How To Track Heart Rate Using Your Mobile Camera
Open Google Fit app on your mobile.
If your device recevied tha update, then click on "Check your heart rate" option on the home page
Now place your fingertip over your back camera lens on your mobile. Also you can turn on the flashlight.
Then you can see a message "Detecting the pulse in your fingertip. Keep your hand still and apply light pressure."
App takes almost 30 to 35 seconds to measure the heart rate.
You can also save your heart rate result, just click on "Save measurement" button.