Push-to-talk (PTT), also known as press-to-transmit, is a method of having conversations or talking on half-duplex communication lines, including two-way radio, using a momentary button to switch from voice reception mode to transmit mode. Push-to-talk (PTT), also known as press-to-transmit, is a method of having conversations or talking 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/her supervision. Those under the same frequency can hear others' transmissions while using procedure words such as 'break', 'break break' to separate order during the conversation (ICAO doc 9432).In doing so, they are aware of each other's actions and intentions, and do not hear any background 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 scenarios requiring coordination of several parties. Citizens Band is another example of classic push-to-talk operation.