A motion sensor includes a piezoelectric transducer and a ball positioned against the transducer, with the ball rollably engaged with the transducer. The transducer generates an electrical signal in response to motion of the ball on the transducer. In a preferred embodiment, the transducer includes a...http://www.google.com.au/patents/US5523644?utm_source=gb-gplus-sharePatent US5523644 - Piezoelectric motion sensor
