A wireless interface circuit can include an electrical relay circuit that is configured for coupling to a separate wired thermostat circuit that is separately housed apart from the wireless interface circuit, where an input to the electrical relay circuit is configured for coupling to an electrical conductor provided between the separate wired thermostat circuit and the electrical relay circuit. A processor circuit is electrically coupled to the electrical relay circuit and is configured to control a state of the electrical relay circuit based on messages received via a wireless interface from a local system located at a location of a customer of an electrical service provider.