Movement detector

A movement detector comprising a pair of flat plates of semi-rigid material supported spaced apart by separator support members secured between said plates adjacent an outer circumferential edge of said plates, a piezoelectric compression transducer secured between said plates substantially centrally thereof, said plates each defining an outer and inner flat surface, a collector one of said plates having a cavity configured in said inner flat surface thereof substantially centrally thereof, said piezoelectric crystal transducer having an electrically conductive backing plate disposed over and bridging a periphery of said cavity, a crystal supported on said backing plate exteriorly of said cavity, an electrode film secured in contact with said crystal, a spacer element of semi-rigid material bridging an outer face portion of said electrode film and said inner flat surface of a supporting one of said plates for concentrating forces on said transducer, a pair of conductor wires connected respectively to said backing plate and said electrode film whereby to generate electric signals when said plates flex with respect to one another by displacement of an exterior load positioned over said top plate, said conductor wires being connected to electronic control circuit means to monitor said signals and to generate alarm signals upon detecting predetermined conditions of said signals, said collector plate and said supporting plate being molded of semi-rigid plastic material, said separator support members being corner posts molded with at least one of said plates and connected to the other of said plates to maintain said plates positively secured in close spaced apart registry with one another, and reinforcing ribs formed integral with said collector plate and supporting plate and protecting from an inner surface of said plates.