Movement detector with mercury switch

Abstract From the Canadian patent

An alert device is provided which initiates an alarm if a person wearing the device ceases normal movement. The device includes a movement sensor having at least one mercury switch which generates a signal when the mercury shifts in response to movement. The device also includes a microcomputer to receive the mercury switch input signals--the microcomputer being programmed to distinguish between inputs indicative of normal wearer movement and inputs which may represent a wearer in duress. Preferably the motion sensor provides three mercury switches oriented to sense movement in three normal planes.