The rain and freeze sensor for sprinkler controllers is engineered to automatically detect rainfall or low-temperature conditions and turn off a sprinkler controller until normal watering conditions return. It has water-absorbing disks which expand when wet, causing the controller to suspend watering. When the disks dry out and contract the controller returns to the normal watering schedule. It is adjustable so you can change the threshold for triggering a delay. It uses a thermistor to detect low temperatures and similarly suspends and restarts watering. You will typically mount the sensor on an eave or other open-air area, and a wire runs up to 30 ft. to the rain sensor port of the irrigation controller. Compatible with 24 VAC controllers from Orbit, Hydro-Rain, and other major irrigation brands.