Theres no need to babysit your de-icing cable. Roof Sentry RS2 measures both temperature and moisture to turn the system on or off in response to changing weather conditions. This automatic control is ideal for cottages and other buildings that have irregular occupancy, as well as for people who have better things to do than to plug and unplug their de-icing cable all winter long. Roof Sentry RS2 is a residential grade unit that energizes de icing cable when two conditions are present cold temperatures (on at 3 degree Celsius/38 degree Fahrenheit, off at 9 degree Celsius/48 degree Fahrenheit) and the presence of runoff water from the roof in contact with the sensor wire. If only one of these conditions exists, the control does not energize the cable.