Control apparatus (1) for selectively applying a mains AC electrical supply (3) to an electrical appliance (4) in response to a remote signal received via a cellular telecommunications network comprises a housing (8) within which an electrical socket (14) for providing power to the appliance (4) is integrally formed. An electrical plug top (10) on a cable (12) extending from the housing (8) is provided for coupling to the mains supply (3). A switch circuit (15) under the control of a microcontroller (19) controls the mains supply (3) to the electrical socket (14). A communications circuit (20) which is adapted for communicating with a cellular telecommunications network receives SMS control messages, and the microcontroller (19) is responsive to the SMS control messages for in turn operating the switch circuit (15) to selectively switch the mains supply (3) to the appliance (4). A power supply circuit (28) independent of the mains supply (3) powers the control apparatus (1). A volt meter (22) monitors the presence of the mains supply (3) and an amp meter (24) monitors the current being drawn by the appliance (4). The microcontroller (19) is responsive to the volt meter (22) detecting the mains supply and the amp meter (24) detecting the absence of current being drawn by the appliance (4) when the switch circuit (15) is in the closed circuit state for determining the operational status of the appliance as faulty.