Rain sensor

The second is a device used to protect the interior of an automobile from rain and to support the automatic mode of windscreen wipers.

An infrared light shone at a 45-degree angle on a clear area of the windshield is reflected and is sensed by the sensor inside the car.

Rain sensors for irrigation systems are available in both wireless and hard-wired versions, most employing hygroscopic disks that swell in the presence of rain and shrink back down again as they dry out — an electrical switch is in turn depressed or released by the hygroscopic disk stack, and the rate of drying is typically adjusted by controlling the ventilation reaching the stack.

Wireless and wired versions both use similar mechanisms to temporarily suspend watering by the irrigation controller specifically they are connected to the irrigation controller's sensor terminals, or are installed in series with the solenoid valve common circuit such that they prevent the opening of any valves when rain has been sensed.

Some type of sensor is required on new lawn sprinkler systems in Florida,[1] New Jersey, Minnesota,[2] Connecticut and most parts of Texas.

The first such device appears to have been used for that same purpose in a concept vehicle designated Le Sabre and built around 1950–51.

General Motors' automatic rain sensor for convertible tops was available as a dealer-installed option during the 1950s for vehicles such as the Chevrolet Bel Air.

[4] In December 2017 Tesla started rolling out an OTA update (2017.52.3) enabling their AP2.x cars to utilize the onboard cameras to passively detect rain without the use of a dedicated sensor.

[5] The most common modern rain sensors are based on the principle of total internal reflection.

Part of the light beam is transmitted through the glass, and the intensity measured for reflection is lower: the system detects water, and the wipers turn on.