This product includes:
1x HC-SR04 Ultrasonic Sonar Distance Sensors
 
This sensor is fast and fairly easy to use. It works at about 2cm to 400cm away, but  10cm-250cm will get you the best.  It equires powering from 5V for best results: connect GND (ground) and VCC to 5V power. While the Trig signal can be 3V or 5V, the 'return' Echo signal is 5V logic.