A door phone or door bell phone is a set of electrical and electronic elements used to handle two-way communication (street to home) in houses, apartments or villas. The device is connected to a secure communication system used to control the opening of the door giving access to any kind of buildings, offices, or apartment blocks. They are so widely used in the mentioned structures, that nowadays, they form part of the standard electrical installation of most buildings.
The simplest version is a simple intercom that establishes a communication between the street door and the house. In buildings where there are more than one door phone plate (located at the outside of the building's door entrance) has a certain number of buttons, depending on the number of flats existing in each building, in addition to the loudspeaker.
A door phone in its most basic version is a two-way intercom allowing communication from the street to the house, with the possibility of driving an electric strike to unlock and open the door, allowing access to the interior of the building.
In places where there is more than one dwelling, the caller street, also called Push Plate or simply Plate Street , is composed of a number of buttons is (usually one per housing) with the label next to the house or apartment number or name of the tenant.
The door phone plate is located at the outside of the entrance of each building, is composed by a matrix of buttons each of them driving a Buzzer located in a unit inside each home, which has a button to activate the electric strike.
There are several installation systems, the most traditional of the 4 + 1, (I.E.: four wires for power, communication and door system and one for the call).
Video door phones
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.
Access control systems. Some manufacturers have also adopted the possibility of opening the door via a keyboard. By introducing a numerical secret code the electric strike is operated. Although there is also the possibility of being used as an access control with either a magnetic card or a smart card.
Among other classifications there is one with three different types of door phones that differ mainly in the number of wires required in their installation, having some parallelism between different manufacturers, that use different communication protocols but a similar wiring topology:
- Conventional: This system is characterized by the use of four wires plus of wires for each home. That is, (4 + "n") wires, where "n" indicates the number of homes. This system is best suited for medium-sized buildings.
- Simplified: This system is characterized by using a wire pair, plus the number of homes in threads. That is, (1 + "n") wires, where "n" indicates the number of homes. It is best suited for medium-sized buildings with two or three entrance gates.
- Digital: This system more suitable for use in large buildings or complex installations, as it ensures maximum capacity and ease of installation. It is characterized for using only two wires for all facilities.