Senor Gruber has uncovered a trick inside Google's Mobile app that uses an undocumented method to access the iPhones proximity sensor. In normal situations, the iPhone proximity sensor - the little thing in the top of the iPhone that knows when you have it up to your face - can be turned on or off. When it's on and you place the phone up to your ear the screen stops responding. When it's off, the sensor does nothing. This is key because no information is passed during this on or off toggle. There is no way to tell if the proximity sensor has been triggered.