Abstract: A movement detector for sensing movement from an infant lying on a mattress whether the infant is awake or asleep. The movement detector is comprised of a piezoelectric transducer secured between a pair of plates with a collector one of the plates having a bore or cavity configured in an inner flat surface thereof at the center of the plate, and with the backing plate of the transducer being secured about the cavity. A spacer element between the center of the transducer and the bottom plate, concentrates the movement forces on to the transducer. Electronic control circuits are provided to monitor the signals generated by the transducer to detect predetermined conditions of the signals in response to movement of the infant placed on the mattress.