Capacitive Rain Sensor Module - 

A rain sensor in which a relay connects if the completely insulated sensor plate gets wet (e.g. raindrops). In contrast to rain detectors with a metallic sensor, this sensor functions capacitively. That means it also switches when getting into contact with distilled water (completely clean rain). Skylights may then be closed with it, canvas blinds may be pulled in or rain is just indicated. 2 installed LEDs indicate the function and the sensitivity is adjustable.