Wanted to eliminate the need of keys to get into my apartment, and this was the cheapest way to do so. Using Home Assistant to controll this, but you can use this with any MQTT service you would like.
Built this using:
And made a custom 3D printed case to fit over our intercom. This case is really badly designed, but it works. You could probably mount the case with some double sided tape, to avoid making holes in the wall.
Proof of concept:
First case prototype:
Finished product:
The code is also really badly made, but if it works, don't fix it, right? Here it is!