An intercom provides two-way audio or video between a door and someone inside, and usually a release for the door. Modern units run on the network, so a door station, an indoor station and a phone app can share one system, and the entry can be logged with the camera.
The intercom is the part of a door system people actually talk to. Its usefulness at a busy entrance depends on audio quality, call handling and where the calls land.
Stations, handset or app
A door station carries the button, microphone and camera. It rings an indoor station, a reception console or an app, and the answer releases the strike or magnet.
Audio and accessibility
Wind and traffic defeat cheap outdoor microphones. Plan the mounting height, any hearing assistance or visual indication, and a fallback for visitors without a phone.