See People Electrically

Researchers at University of Utah has showed off an awesome application of radio tomographic imaging. It detects the position of a human by sensing electric fields.

Source links: Radio Tomographic Imaging at SPAN
http://span.ece.utah.edu/radio-tomographic-imaging
http://span.ece.utah.edu/
http://www.redorbit.com/news/technology/1768085/radio_waves_see_through_walls/index.html

See also:
MIT Electric Field Imaging - "Seeing" by Inverse Electrostatics
Intel implements robots that sense before they touch