title: how does the iphone app Cardiographdetect heartbeat?
body: <p>Here is some info of the cardiograph app if you dont know it:
    <a href="http://www.spotlightofpeace.com/techarea/photos/cardiograph-application-to-measure-heartbeat-from-iphone-and-ipad-camera/" rel="nofollow noreferrer">http://www.spotlightofpeace.com/techarea/photos/cardiograph-application-to-measure-heartbeat-from-iphone-and-ipad-camera/</a></p>
  
  <p>Looks like it is senses the light. I know here is some discussion of ambient light sensor:   <a href="https://stackoverflow.com/questions/6408840/about-ambient-light-sensor-in-iphone">About Ambient Light sensor in iphone</a></p>
  
  <p>but not sure if this app uses this sensor, does anyone know better about this?</p>