Push-to-talk (or press-to-talk) is a two-way communication method that uses half-duplex mode where transmission occurs in both directions, but not at the same time. To use PTT, users must press a button on the PTT device while speaking, then release it when done. The listener must then do the same to respond. Common PTT devices include the walkie-talkie. Newer PTT systems use VoIP to provide digital PTT service over 3G data networks.