Microsoft Research develops sound based gesture system
SoundWave, developed by Microsoft Research and the University of Washington, is a real-time sensing technique that leverages a speaker and a microphone to robustly sense in-air gestures and motion around a device. It is capable of detecting a variety of gestures, and can directly control existing applications without requiring a user to wear any special sensors.
It makes use of the doppler effect, which describes the change in frequency as a result of relative motion between a sound source and a listener. The technology leverages existing audio hardware found in almost all mobile devices and so could well find uses in masses of applications aside from sitting in a coffee shop waving at your laptop!
Whilst the video demonstration is limited to a laptop for standard use, I could see this finding great application in areas where present IR based visual gesture technologies (like Kinect) currently struggle – such as shop windows with a lot of background movement and high levels of background IR from the sun.