We live in an apartment building with a shared analog intercom (Elvox). I never used the handset, so I ripped it out and replaced it with something useful. The intercom still works normally for all the other residents.

Doorbell: A Shelly Plus Uni sits inside the intercom wiring. It counts the ring signal and its relay is wired in parallel to the door opener button. When someone rings, a chime plays on all Sonos speakers as an audio clip, so music keeps playing and groups stay intact. I also get a notification in Apple Home.

E-paper panel (CrowPanel 5.79", ESPHome) next to the apartment door:

Clock, outside temperature, today's forecast, rain chance for the next 2 hours

Window status ("All windows closed" or which one is open)

What's still on: lights, music, TV

Waste collection reminder the evening before

Next bus, already counting the walk to the stop: "leave in 5 min"

Three stainless steel buttons:

Front door: buzzes the building entrance

Cellar: unlocks the smart lock on the cellar door, which…