The Rain Tracker automotive rain sensor, senses rain or snow hitting the windshield, and automatically runs the wipers at the right speed. we don’t have to take our hands off the wheel, or constantly adjust the speed of the wipers as road conditions change. A rain sensor or rain switch is a switching device activated by rainfall In this the sensor projects infrared light into the windshield at a 45-degree angle If the glass is dry, than most of this light is Reflected back into the sensor by the front of the windshield.If water droplets are on the glass, than it reflect the light in different direction…the wetter the glass, the less light makes it back into the sensor. The electronics and software in the sensor turn on the wipers when the amount of light reflected onto the sensor. software sets the speed of the wipers based on how fast the moisture builds up between wipes. It can operate the wipers at any speed. we don’t have to take our hands off the wheel, or constantly adjust the speed of the wipers as road conditions change.