HC-SR04 Ultrasonic Sonar Distance Sensor
Buy 10 and save 10%:€4.90 €4.05
HC-SR04 Ultrasonic Sonar Distance Sensors work at about 2cm to 400cm. You will get you the best results at 10cm-250cm.
These sensors are fast, fairly easy to use, and low cost. They do require 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.