An intercom, talkback, or intercom is an autonomous voice communications system for use within a building or small collection of buildings, operating independently of the public telephone network (Azori 2016). Intercoms are usually permanently mounted on buildings and vehicles. Intercoms can incorporate connections to public speaker system loudspeakers, walkie talkies, telephones and other intercom systems. Some intercom systems incorporate control of devices such as signaling lights and door locks.
There are simple intercoms and intercoms for collective apartments. Some are equipped with video, and their wiring (electrical installation), can be connected to the outside with few pairs (4-6 pairs) while controlling an electric shock. The latest generations are even compatible with computers and some models include TCP / IP.
Traditional intercom and public address systems are made up entirely of analog electronics, but many new features and interconnection options can be achieved with new intercom systems based on digital connections. Video signals can be carried as well as voice. Digital intercom stations can be connected via the Cat 5 cable and can even use existing computer networks as a means to connect to distant parts.
Many schools and office buildings now use audio / video systems to identify visitors who seek access to a closed building and can be connected to the building's access control system. In addition to fixed locations, intercom systems are used in many types of vehicles, including trains, boats, airplanes and armored combat vehicles.