Abstract: A target tracking transmitter has an internal voltage supply which may be operated at a first operative level and a second reduced operative level. A switch is provided for cycling the voltage supply between the first and second operative levels, which are both sufficient to ensure generation by the transmitter of radio frequency signals for detection by a remote receiver. The switch is arranged to control the time for which the transmitter is cycled at the first and second levels whereby the operating life of the internal voltage supply is maximized while enabling continuous generation of the radio frequency signals.