Gesture Control System Uses Sound Alone
From: Technology Review - 05/07/2012
By: Rachel Metz 

Microsoft researchers have developed SoundWave, a gesture-control system that
utilizes the Doppler Effect, software, and the built-in speakers and
microphone on a laptop. The technology can be used to sense several simple
gestures. Speakers equipped with SoundWave software emit a constant
ultrasonic tone of between 20 and 22 kilohertz. If there is no movement in
the immediate environment, the tone the microphone hears should be constant.
However, if something is moving toward the computer, that tone will shift to
a higher frequency. If something is moving away, the tone will shift to a
lower frequency. This phenomenon happens in predictable patterns, so the
frequencies can be analyzed to determine how big the moving object is, how
fast it is moving, and the direction it is going, says Microsoft's Desney
Tan. The software currently performs with about 90 percent accuracy,
according to the researchers, who have developed several movements that the
software can understand, including swiping your hand up or down, moving it
toward or away from your body, flexing your limbs, or moving your entire body
closer to or farther away from the computer. 

Read the entire article at:
http://www.technologyreview.com/web/40368/

Links:
Researchers Add Sound-Based Gesture Recognition to Commodity Computer
http://thejournal.com/articles/2012/05/08/researchers-add-audio-based-gesture-recognition-to-commodity-computer.aspx

Soundwave
http://research.microsoft.com/en-us/um/redmond/groups/cue/soundwave/

Desney Tan
http://research.microsoft.com/en-us/um/people/desney/

Microsoft creates Kinect-like system using your laptop’s built-in speaker
  and microphone
http://www.extremetech.com/computing/128735-microsoft-creates-kinect-like-system-using-your-laptops-built-in-speaker-microphone