The WSG Wireless Temperature sensor is designed to work exclusively with the Sensaphone WSG30. This sensor includes a built-in radio transmitter and temperature element for monitoring temperature wherever the device is installed. You can remove the internal temperature element and attach a remote temperature probe so that measurements can be made in a refrigerator, freezer or other harsh environment. 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 in which case the batteries become a backup if main AC power fails.