Ultrasonic Sensor HC-SR04

Power supply: 5V DC
Resting current: <2mA
Effective angle: <15 °
Resolution: 3mm
Range: 2cm-500cm

There are 4 pins on the Ultrasonic Sensor HC-SR04
Vcc: 5V DC Power supply
Trig: Sends the signal
Echo: Receives the signal
Gnd: Ground

By calculating the time between sending and receiving you can determine how far the sensor is removed from an object.