Ever wonder how your car knows it’s raining—and even how hard? Most rain-sensing wipers use a sensor that’s mounted behind the windshield. It sends out a beam of infrared light that, when water droplets are on the windshield, is reflected back at different angles.
This tells the system to activate the wipers, as well as adjust wiper speed and frequency based on the intensity of the precipitation combined with the vehicle’s speed. That’s a convenience and potentially a real safety benefit when driving through heavy rain on a dark highway.