Do Kinect-like things on your computer, but without the Kinect: the technique uses your speakers and microphone to sense what gesture you are making.
Called SoundWave, the new technology uses the Doppler effect to detect any movements and gestures in the proximity of a computer. The Doppler effect, if you remember high school physics, is where the frequency of a sound alters depending on your distance from it. In the case of SoundWave, your computer’s built-in speaker is used to emit ultrasonic (18-22KHz) sound waves, which change frequency depending on where your hand (or body) is in relation to the computer. This change in frequency is measured by your computer’s built-in microphone, and then some fairly complex software works out your motion/gesture.
(RT’d by @lukew)