This kit is useful for detecting movement within 4m range in a 40 degree cone in front of the sensor. A matched pair of ceramic transducers, operating at 40 kHz is used for sensing. No calibration is needed since a 40 kHz crystal oscillator drives the circuit at the optimum frequency of the transducers. Sensitivity is adjustable. A LED lights up and a transistor output goes low when movement is detected. Operating Voltage: 9 - 12Vdc