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.

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But our experts say there’s room for improvement: It’s even better when the automatic headlights turn on at the same time as the wipers, because in some light conditions, the driver may not notice they are not on and many states require the lights to be on when the wipers are in use. Some newer cars do smartly connect wiper operation with the automatic headlights. This is a feature worth asking about when car shopping.

Rear wipers on SUVs and hatchbacks are manually controlled because there isn’t the same need to keep the back glass clear when driving. Many modern vehicles will activate the rear wiper when the front wipers are on and the transmission is shifted to Reverse.  

From the 'Consumer 101' TV Show

Today's cars come with cutting edge safety technology that can stop working with one simple thing: dirt. Consumer Reports' expert show on 'Consumer 101' where these important safety sensors are on a car and how to keep them clean.