An electronic device for indicating an abnormal condition in a rotatable member. A typical use for such a device would be for the detection of a low pressure condition in a tire on a vehicle. In the preferred form for this typical use, a reflecting surface, such as a mirror, is affixed to the wheel and...http://www.google.es/patents/US4086564?utm_source=gb-gplus-sharePatente US4086564 - Electronic alarm circuitry
