WSG Wireless Dry Contact Sensor Description The WSG Wireless Dry Contact sensor is designed to work exclusively with the Sensaphone WSG30. This sensor includes a built-in radio transmitter and input terminals for connecting to any normally open or normally closed output. (Use of this device with solid-state outputs is not recommended.) The sensor comes with two AA alkaline batteries which will power the sensor for up to two years. An optional plug-in power supply is also available. The batteries then become a backup if main AC power fails.