The HY-SRF05 Ultrasonic Range Finder Module uses ultrasonic sound waves to detect the presence of and measure the distance to objects in front of it.
The detection and measurement range is from 2 cm up to 450 cm which is about 15 feet with a stated accuracy of +/- 2mm. The ultrasonic sound is pulsed at 40 kHz and is not audible to the human ear. The HY-SRF05 is a higher precision version of the HC-SR04, but otherwise is similar.
These modules are commonly used on robotic vehicles for obstacle detection and avoidance. Because they use sound waves for detection they are not sensitive to light sources or optically reflective surfaces like IR can be. In addition, by using sound instead of light, it is possible to measure the time that it takes for the sound to be echo?d back and therefore the distance to the object can be calculated with a fair amount of accuracy which can be quite handy.
These modules have a ?view? of about 15 degrees, so they are sometimes mounted to a servo motor so that the sensor can ?look-around? at its surroundings. The fact that the sensors look like a couple of eyes adds to the cool factor as well.