Communication circuit for 2-wire protocols between HVAC systems and smart-home devices

A circuit for stealing power from an external system without interfering with a communication protocol may include wiring connectors configured to receive wires from the external system; a first voltage regulator to regulate a voltage on the plurality of wiring connectors at a plurality of voltage levels to encode a first multi-bit binary message according to the communication protocol to be sent to the external system; a current monitor to measure a plurality of current levels received through the plurality of wiring connectors and decode the plurality of current levels to determine a second multi-bit binary message sent from the external system according to the communication protocol; and a power converter that adjusts an amount of power stolen from the plurality of wiring connectors based at least in part on the voltage on the plurality of wiring connectors.