This is a puredata patch which implements
an 'ultrasonic theremin'.
High-frequency chirps are played over the laptop speakers, and the reflected audio signal is received by the built-in microphone (above the keyboard on this particular notebook model). The puredata program calculates the time that was needed for the sound to be echoed back and drives a simple tone generator to create a sound. The resulting sound is played over the same speakers as the ultrasonic chirps.
The second video shows a simple OpenGL game controlled by ultrasone.
DownloadGet the patch here: ultrasonic_theremin.pd
Important note: Puredata needs to be running on a samplerate of at least 88200 HZ to allow the high-frequency chirps to be played and recored. The patch was only tested on a Dell D830, it might or might not work on other hardware.