Start with the iPhone, work back to human nature.

"MIT Technology Review put a brief article up at the end of June describing some of the unrealized potential in the iPhone. Turns out that, in addition to having the interface to kill all portable interfaces, it is tricked out with a number of just slightly utilized sensors; specifically an accelerometer, an ambient light meter, and an IR motion sensor. While Apple has applied these to the admirable goal of rotating your screen and adjusting your brightness for you, some other smart people have already been busy using them for more creative ends. Like learning about human nature."