Abstract: A motion sensor system is provided that has several sensor units. Each sensor unit is freely movable, easily hidden and includes a motion sensor and a wireless radio frequency (RF) transmitter. The motion sensor system further includes a receiver unit, which includes a wireless radio frequency receiver and a device for communicating receipt of a signal to the user. When at least one of the motion sensors of at least one of the sensor units detects motion, the wireless radio frequency transmitter transmits a signal to the radio frequency receiver of the receiver unit. The receiver unit then communicates receipt of the signal to the user.