Aukru 3pcs HC-SR04 Ultrasonic Module Distance Sensor for Arduino UNO Mega R3 Mega2560 Duemilanove Nano Robot Xbee Zigbee Ultrasonic Module HC-SR04 Distance Measuring Transducer Sensor for arduino uno r3, mega, raspberry pi Working Voltage: 5V DC; quiescent current: &lt; 2mA; effectual angle: less than 15; distance: 2cm~400cm; resolution: 0.3 cm Output signal: Electric frequency signal, high level 5V, low level 0V HC-SR04 consists of ultrasonic transmitter, receiver, and control circuit. When trigged it sends out a series of 40KHz ultrasonic pulses and receives echo from an object. Test mode :Using IO trigger for high level signal.( Not less that 10us),The Module sends eight 40 kHz automatically and detect whether there is a pulse signal back.