Smart phones are getting amazing.
Been using this an app to track my heart rate at the gym and it's really accurate as I tested it against what the doctor tracked my heart rate when I was doing a stress test. It uses the camera's LED light to make your finger tip glow and then uses the camera to measures the change in color as your finger gets oxygenated with each heart beat to figure out your heart rate.
http://www.instantheartrate.com/