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 can incorporate connections to public address loudspeaker systems, walkie talkies, telephones, and to other intercom systems. 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. Traditional intercoms and public address systems are composed entirely of analogue electronics components but many new features and interfacing options can be accomplished with new intercom systems based on digital connections.