Most gesture recognition systems are based on line of sight and thus limits their capabilities despite recent advances (Xbox Kinect). A few folks at the University of Washington have realised a gesture recognition system from what could’ve only stemmed from science fiction or stupendously imaginative mind. The concept is pretty straight forward, and I ‘d wager that it would very unlikely be feasible in the near future. Still, just the fact that something like this is possible is amazing (while the rest of the world still hungers for needlessly large smartphones or monstrously high resolution screens) and stands out in what has become a stagnant age for technology where people would rather battle for ridiculous patents.
The simplest analogy that I can provide as to how the system works, is to think of radar with an extrapolation of patterns and time. Just with disturbances in radio frequency signals on the WiFi spectrum, it is possible to recognize gestures.