A medical device, for use inside a body of a mammalian subject, includes a casing adapted for insertion into the body of the mammalian subject, the casing having an outer surface and including an insulating material and an electrically-conductive material, which are arranged so that an area of the outer surface of the casing is electrically conductive. A transmitter is adapted to generate an electrical signal and is encapsulated in the casing and coupled to the conductive material so that the electrically-conductive area of the outer surface serves as an antenna for transmitting the signal to a receiver outside the body.