A walkie-talkie (more formally known as a handheld transceiver) is a hand-held portable, two-way radio transceiver. The first walkie-talkies were developed for military use during World War II, and spread to public safety and eventually commercial and jobsite work after the war. Major characteristics include a half-duplex channel (only one radio transmits at a time, though any number can listen) and a push-to-talk switch that starts transmission. Typical walkie-talkies resemble a telephone handset, possibly slightly larger but still a single unit, with an antenna sticking out of the top. Where a phone’s earpiece is only loud enough to be heard by the user, a walkie-talkie’s built-in speaker can be heard by the user and those in his immediate vicinity. Hand-held transceivers may be used to communicate between each other, or to vehicle-mounted or base stations.
Since even a powerful commercial walkie-talkie is limited to a few watts of power output and a small antenna (the physical size of the package limits both battery capacity and antenna size), hand-held communication range is typically quite short, not exceeding the line-of-sight distance to the horizon in open areas, and very much less in built-up areas, within buildings, or underground. Many radio services permit the use of a repeater which is located 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.
Some cellular telephone networks offer a push-to-talk handset that allows walkie-talkie-like operation over the cellular network, without dialing a call each time.
Walkie-talkies for public safety, commercial and industrial uses may be part of trunked radio systems, which dynamically allocate radio channels for more efficient use of limited radio spectrum.