Acoustic Gesture Recognition
This Acoustic Gesture Recognition by Gary Halajian and John Wang from the Cornell University Designing with Microcontrollers course reminds me of the Object Scratching Input Device that Chris Harrison made (I later read the references and see that sure enough they reference the Object Scratching Input Device Project). "Our project utilizes a microphone placed in a stethoscope to recognize various gestures when a fingernail is dragged over a surface.