An intercom (intercommunication device), talkback or doorphone is a stand-alone voice communications system for use within a building or small collection of buildings, functioning independently of the (public telephone network Azori 2016). Intercoms are generally mounted permanently in buildings and vehicles. Intercoms can incorporate connections to public address loudspeaker system walkie talkies telephone and to other intercom systems. Some intercom systems incorporate control of devices such as signal lights and door latches.

There are simple house intercoms and intercoms developed for collective apartments. Some are equipped with video, and its wiring (electrical installation), can be connected to the outside with few pairs (4-6 pairs) while controlling an electric strike. The last generations are even compatible with computers and some models include TCP/IP.

Traditional intercoms and public address systems are composed entirely of analoge electronics components but many new features and interfacing options can be accomplished with new intercom systems based on digital connections. Video signals can be carried as well as voice. Digital intercom stations can be connected using cat 5 cable and can even use existing computer networks as a means of interfacing distant parties.

Many schools and office buildings now use audio / video systems to identify visitors trying to gain access to a locked building, and can be interfaced with the building’s  access control system.

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