SoundWave:
Using the Doppler Effect to Sense Gestures

SoundWave, a technique that leverages the speaker and microphone already embedded in most commodity devices to sense in-air gestures around the device. To do this, we generate an inaudible tone, which gets frequency-shifted when it reflects off moving objects like the hand. We measure this shift with the microphone to infer various gestures.

http://research.microsoft.com/en-us/...cue/soundwave/

Though the scrolling gestures are not convincing, I still think there's a lot of potential to it. Maybe even as an accessibility technology. How about a responsive smartphone for the blinds to warn or guide them? Or acting like a ray gun, vibrating to give out obstacles and the distance to them?