Microsoft Research's SoundWave is an experimental interface that detects gestures based on how movements of your hand interfere with an inaudible tone generated by the computer. It doesn't use the same operating principal as the Theremin but it reminds me of that famous "hands-off" musical instrument. "SoundWave: Using the Doppler Effect to Sense Gestures" (Thanks, Lyn Jeffery!)
David Pescovitz is Boing Boing's co-editor/managing partner. He's also a research director at Institute for the Future. On Instagram, he's @pesco.