Remember when you purchased your first iPhone, received your first telephone call on it and were entirely perplexed when the screen turned itself off every time you raised the device to your head during the call? I certainly remember getting the original iPhone in 2007 and believed the behavior based on the inclusion of the proximity sensor was nothing short of with craft. As I learned more about the device it became obvious that switching the display off in those circumstances was a pretty clever idea and now thanks to a new tweak users can invoke that functionality at will through a pre-defined gesture.