Sunkee 16mm 40khz Waterproof Ultrasonic Sensor Receiver Transmitter R and T in one Diameter: 16 mm Center Rated Frequency: 40 KHz Sound Pressure Level (at 10V): 117 dB Receiver Sensitivity (at 40KHz): -65 dB 1 X 16mm 40khz Waterproof Ultrasonic Sensor Receiver Transmitter R and T in one