A high sensitivity ultrasonic transmitter & receiver sold only in pairs for sending & receiving ultrasonic sound through the air either as a continuous wave or pulses. Applications include burglar alarm systems proximity switches liquid level meters anti-collision devices counters for moving objects TV remote control systems etc. Specifications T-40R-40 Transmitter Receiver SPL91W1m 120d B-Sensitivity 5m VPA1k Hz 5m VPA1k Hz Resonant freq. 40 K Hz plusmn 140 K Hz plusmn 1 Max. input 20 Vrms Capacitance p F plusmn 2024002400 Overall size 16mm dia x 12mm deep connecting pins protrude a further 9mm pins are 10mm apart.