A locking device is provided for an electrical socket. The locking device includes a device body having a projecting member projecting from the device body, wherein the projecting member is adapted for engagement with an aperture provided in an electrical socket. The projecting member has first and second positions. In a first position the projecting member is adapted for engagement with the aperture and the locking device can be connected and disconnected from the socket. In a second position, the projecting member cannot disengage from the aperture and the projecting member is lockable in the second position. The electrical socket may be a power cable receiver on an electrical appliance, or a power supply socket.