New submitter brunozamborlin writes "I just published a short video that shows how a very cheap contact microphone can be used to recognize different types of fingers touch and transform any surface into an interactive board. In the video we put the microphone over different surfaces such as kitchen tables and balloons and through realtime gesture recognition we show how we can play different virtual music instruments using a technique called physical modeling . A mobile version would be definitely possible." The project's Web page shows several more examples. Update: 12/31 15:17 GMT by T : Bruno Zamborlin points out that the surfaces don't need to be flat; instead, they simply need to be rigid.