Door phone

They are so widely used that, nowadays, they form part of the standard electrical installation of most buildings.

[1] The simplest version is an intercom that establishes a communication between an entryway at street level and a resident inside the house.

A loudspeaker installed at the street level entrance allows a building resident to speak to their visitor.

A door phone in its most basic version is a two-way intercom allowing communication from the street to the inside of a building.

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.