With the walkie talkie’s development, even the powerful commercial walkie-talkie is limited to only a few watts of power output and hand held communication range is still quite short in open areas. Many radio services permit the use of a repeater (which is a device that increases range and coverage of a walkie talkie) which is usually placed at some high point within the desired coverage area. The repeater listens on one frequency and retransmits on another, so that reliable hand-held to hand-held unit range can be extended to a few score miles (kilometers) or further, using repeaters linked together.