Neither of those will work from what I can see. You can't mix the inputs and outputs like that. In fact, your existing button probably should not even be touched in this setup. You are misunderstanding how to wire this.
In my opinion, this Shelly device isn't really suited for this task. It is overly complicated, and doesn't appear to have just a set of relay contacts which are what is needed here. There are easier to wire devices like this device that don't require a bunch of farting around for the same price. Amazon.com
That being said, do you have a digital multimeter, and do you know how to use one? If so, I can probably guide you through this.
The problem here is that the UNI does not have dry contacts (mechanical relays) and what they use to switch is 100mA Max, most of the time a "buzz in door system" uses a mechanical electro magnet and many older ones are directly connected to the button in each apartment, these things will pull a lot more than the 100mA the UNI can deliver and is most likely the problem here. If you want to use the UNI, you should get a low power relay to wire in between the UNI and the door "buzzer". Just make sure the relay does not need more than 100mA to engage and be sure to get a mechanical one.
Absolutely agree. Until now, every time I tried to get something done with the Shelly Uni, it just got complicated and never brought me the result I've wanted...
Yeah, I got one and know how to use it. If you could help me, that would be awesome.
I didn't see that this was an apartment door buzzer until I re-read it and with what @nclark said above.
You will need to do what he said and get a relay that isolates this device from your door system, and to carry the load of this door device. This shelly is not suitable by itself for this task, it will likely burn up (if it hasn't already) by trying to use this as a standalone device.
But looking at the MHCOZY, it should do the trick. It has dry contacts, and when I look at the advertisement, door security systems, closing systems etc. are listed. So it should work, right?
I've tried the MHCOZY today. It was a direct success. Just plug and play.
Edit:
For readers later on; In my case, the regular door buzzer stopped working, as soon as I connected the MHCOZY, for what ever reason. To keep the regular door buzzer-function, a used the manual switch, which is connected to the relay. I put everything into a box and squished a plastic button over the switch to access it.
The MHCOZY was set to switch mode. Within Hubitat, I quickly wrote a rule, turning the switch off, three seconds, after it was turned on. This keeps the regular buzzer function, with more than enough time to enter the building.
Using the Hubitat Dashboard from @jpage4500, I quickly created a widget on my smartphone, for a quick access (don't forget to enable cloud mode). Now I don't need a key anymore, to get into my building.
