A control device may comprise a primary radio circuit for receiving radio-frequency signals via an antenna, and a secondary radio circuit for waking up the primary radio circuit when a radio-frequency signal is presently being transmitted by an external device. The control device may include a control circuit that may be coupled to the primary radio circuit, and may control the primary radio circuit into a sleep mode. The secondary radio circuit may generate a first control signal indicating that the radio-frequency signal is presently being transmitted by the external device. The control circuit may wake up the primary radio circuit from the sleep mode in response to the secondary radio circuit generating the first control signal indicating that the radio-frequency signal is presently being transmitted by the external device.