Link a raspberry to an intercom

[Matador3k]

Hello,
I want to connect a raspberry to my intercom.
I think it's pretty simple, but i block on the electronic part: :
1 - The raspberry has to watch if someone ring at the door. I think i can plug it on the intercom buzzer and detect if there is an electrical signal.
2 - If an electrical signal is detected on the buzzer, the raspberry has to open the door by simulating the push of the button, with a relay.
If someone can tell me how to do this !
Thanks.

[SIDF92]

Hello,

I would see the input of your intercom

It may start with a simple push-button...
Use this passive push-button (I mean disconnect the electrical part).
With simple resistor in serie, you should not destroy your RPI using 1 GPIO and a pull-up to +3.3V for example.

Then use another GPIO to command the electrical part of your intercom.
You have to isolate your command !
Relay, optocoupler...and why not SSR (Solid-State Relay) should be sufficient.
Please ask if i'm not clear (my english is quite poor).

SIDF92

PS : Post an enlarged version of your photo. I will draw on it.