Abstract: A portable thermostat is coupled to the control unit of a heating or cooling device through a radio link. The RF signal transmitted by the thermostat is encoded and then decoded by the control unit in order to prevent interference with other similar devices. In order to maximize the life of a battery powering the thermostat, the thermostat calls for the energization of a heating or cooling device by transmitting the RF signal at widely spaced intervals. The heating or cooling device is energized by shunting a pair of terminals, thereby completing an AC control loop. The control unit applies the terminals to a storage capacitor during a small portion of each AC cycle to power the control unit while shunting the terminals during the remaining part of the cycle.