Does anyone know how an old apartment intercom with door unlocker works? When I open it I see 2 wire connected to it.
The way it works is very simple: if someone at the building entrance pushes my name on the button I can hear a buzzer. When I pick up the phone I can talk and I can push a button to release the door.
It seems everything is going through those 2 wires.
Using a voltmeter I can read 13v. And when I push the button it go to 0v.
Any one know more about how this works?