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1980s MirTone intercom system. An intercom, also called an intercommunication device, intercommunicator, or interphone, is a stand-alone voice communications system for use within a building, small collection of buildings or portably within a small coverage area, which functions independently of the public telephone network. [1]
A user could select any available telephone line by pressing the appropriate pickup key and taking the handset off-hook. While on a telephone call, a user could place the call on hold by pressing the hold button, which also released the depressed line button mechanically, enabling the user to select another line for placing a call.
Key was a Bell System term of art for a customer-controlled switching system [1] such as the line buttons on the phones associated with such systems. The electrical components that allow for the selection of lines and features such as hold and intercom are housed in a panel or cabinet, called the key service unit or key system unit (KSU). [2]
For an example, a school is an environment that displays all the capabilities of an intercom telephone. Using an intercom telephone, administrators can make announcements over loudspeakers that are heard by the entire building, but they can also call a specific classroom 's intercom by dialing the room number of that classroom.
Video door phone indoor terminal.. Going a little further in time, we find video door phones featuring a video installation apart from the classical audio. In these cases, the intercom plate has the same structure as the previous version but features a video monitor connected to a surveillance camera that allows inspecting the person who pressed the button and part of the surrounding area.
Outdoor Intercom - This is an intercom that can be placed by a building's doors and it operates like a doorbell, but people inside can talk to the visitor. Channels - Some wireless intercom systems have more than one channel so private conversations can occur between groups of intercoms.
With manual service, the customer lifts the receiver off-hook and asks the operator to connect the call to a requested number. Provided that the number is in the same central office, and located on the operator's switchboard, the operator connects the call by plugging the ringing cord into the jack corresponding to the called customer's line.
In middle 20th century telephone jargon, the first telephone on a line was a "Main Station" and subsequent ones "Extensions" or even called as intercom. Such extension phones allow making or receiving calls in different rooms, for example in a home, but any incoming call would ring all extensions and any one extension being in use would cause ...