Researchers use ambient WiFi radio waves to see through walls
 

Seeing through walls hasn't been a super hero-exclusive activity for a while now. According to Popular Science, however, University College London researchers Karl Woodbridge and Kevin Chetty have created the first device that can detect movement through walls using existing WiFi signals. While similar tech has required a bevy of wireless nodes, the duo has pulled off the feat with a contraption roughly the size of a suit case.

Much like radar, the device relies on the Doppler effect -- radio waves changing frequencies as they reflect off of moving objects -- to identify motion. Using a radio receiver with two antennas and a signal-processing unit, the system monitors the baseline WiFi frequency in an area for changes that would indicate movement. In tests, the gadget was able to determine a person's location, speed and direction through a foot-thick brick wall. The technology's potential applications range from domestic uses to scanning buildings during combat. Best of all, since the university's hardware doesn't emit any radio waves, it can't be detected. How's that for stealthy?

http://www.engadget.com/2012/08/03/r...through-walls/