Pulse Rate uses the iPhone's microphone to determine your heart rate, and keeps track of your heart rate in its stopwatch. Just press the "Take pulse" button, hold the phone's microphone (next to the dock connector) up to your artery, and wait for the phone to vibrate. (Also works with iPhone headphones with mic.) If it is unable to find your heart rate, it won't make you wait longer than 10 seconds before telling you there has been an error.
Pulse rate's built-in stopwatch keeps track of your exercise time and laps, and lists your heart rates with the laps so you can see how your heart rate changes through your workout.
Avoid environments with loud noises.
Avoid moving, which introduces vibrations
Avoid layers that muffle the heart beat.
Resting heart beats are difficult to detect.
***App does not work with iPod Touch 2nd Gen Earphone microphone