An inductive power transmitter comprising a transmission circuit having a coil, the transmission circuit tuned, adapted or optimised at or about a first frequency for inductive power transfer or object detection; an inverter operable to drive the transmission circuit at the first frequency; and a controller arranged to control the inverter to drive the transmission circuit at a second higher frequency, and to modulate a signal at the second higher frequency according to a predetermined handshake signal in order to generate a response from a predetermined non-authorised device proximate the coil.