Push-to-talk (PTT), also known as Press-to-Transmit, is a method of conversing on half-duplex communication lines, including two-way radio, using a momentary button to switch from voice reception mode to transmit mode.

For example, an air traffic controller usually talks on one radio frequency to all aircraft under his supervision. All can hear each other's transmissions and those of the controller, and take turns speaking, using procedure words such as "over" and "out". Thus they are aware of each other's actions and intentions, and do not hear any noise from the ones who are not speaking. Similar considerations apply to police radio, the use of business band radios on construction sites, and other situations requiring coordination of several parties. Citizens Band is another example of classic push to talk operation.

Where a user may be too busy to handle a talk switch, for example in combat aircraft, voice operated switches are sometimes employed. Some systems use PTT ID to identify the speaker.

Push to Talk over Cellular (PoC) is a service option for a cellular phone network which permits subscribers to use their phone as a walkie-talkie with unlimited range. A typical Push to Talk connection connects almost instantly. One significant advantage of PoC / PTT is that it allows a single person to reach an active talk group with a single button press; users need not make several calls to coordinate with a group.

Read more about Push-to-talkMobile Phone, Current Use in Mobile Telephony (PoC), Smartphone/Computer Apps

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Two-way Radio - Types - Push-to-talk
... Products microphone was created with a rocker-style push-to-talk button for Motorola Micro mobile radios ... In two-way radios with headsets, a push-to-talk button may be included on a cord or wireless electronics box clipped to the user's clothing ... consoles often have a hand-operated push-to-talk buttons along with a foot switch or pedal ...