Looking for some guidance with a “dumb” intercom

Hey —

I know there are quite a few posts out there about converting a dumb intercom into a one with some smart capabilities, but I’ve read so many now I’m at a bit of a loss.

My use case: I live in a traditional 3 story walk up, with a front door controlled by an intercom system. Someone presses my doorbell, the intercom buzzes, I can talk/listen and open the door by a press of a button on the intercom panel in my unit.

My goal: I’d like to enhance the door opening functionality, preferably by installing a Shelly 1 (based on what I’ve read, I think this might be my best option). In a best case scenario, I’d also be able to install one into the chime so that I can use that to send a notification when someone buzzes me.

Where I need help:

  1. Here’s the wiring available in my unit: https://i.imgur.com/ozqsyFq.jpg. From reading the user manual for the panel, there’s 3 common wires (one for each button?) and a “Selective 22AWG”. Is the latter what I would need to tap into to power the Shelly? Or do I need to find an additional power source? I’m starting to think the wiring available in my unit isn’t sufficient, and I would need to install in the main panel outside.

  2. Could I use a second Shelly to monitor the bell and therefore send an alert via HA when the bell is triggered? Same question for wiring, is it as simple as tapping into the power supply and wiring used for the bell?

I’m fairly comfortable with most wiring; I’ve replaced quite a few in-wall switches, thermostats, and setup a Konnected.io, but am not sure where to start with relays and would appreciate any guidance or helping me get started in the right direction.

Thanks so much in advance!

If you are going to use shelly, remember that the voltage is Line(120-240v) ac, 24-60v dc and 12v dc. The entire device sees the voltage input. On my fireplace, I used a shelly 1 but had to supply a converter to get to 12v.

I would use a voltage meter and determine the voltage on each wire when doorbell is pressed and when you press the entry button. This will let you know what is happening and you can better determine the hardware you need to make it work.

This video may help you


Thanks so much for your help; took your advice and measured the voltage – looks like ~13.5, but I’m not sure if that’s a “standard” amount. It dropped to about 5 or 6 when the button was actually pressed.

I assume this means the intercom interface in my unit has enough power to tap into to power the Shelly 1? Or is there another relay I should be looking into?

Thanks again

I won’t use power as the criteria as that has to do with current as well (P=V*I). You most certainly have enough voltage. I will refer you to this guide for further assistance. I think you can make this work.

Here is the link.



@stx21 were you able to make this work? I am starting on a similar project, I have the talk/listen/door intercom and I am trying to make it compatible with my home assistant. The main reason is so I can get notifications and buzz, someone, in even when I am not home.