3D ultrasound mouse

http://people.ece.cornell.edu/....land/courses/ece4760
Ultramouse 3D is a spatial human interface device that lets the user interact with computer programs in three dimensions. Ultramouse 3D times the delay of high-frequency sound waves from the unit held by the user to each of three receivers and passes this information along a serial cable to the computer. The accompanying open-source API provides easy functions that let any Win32/C++ application start reading 3d data in less than 5 minutes.