A batteryless sensor includes a small and concealed permanent magnet motor which operates as a generator to convert rotational or translational energy to an ersatz Vcc transient power supply via a mechanical arrangement to radiate a coded VHF oscillator signal to a repeater or central processing unit...http://www.google.co.uk/patents/US5317303?utm_source=gb-gplus-sharePatent US5317303 - Batteryless sensor used in security applications
