That's brilliant! You reminded me of a story from my childhood.

This one time my neighbor rang my doorbell. I answered on the intercom.

We talked for a minute and were then both puzzled. "Why did you ring the bell?"

"I didn't ring the bell. You did!"

Turns out we were both in our apartments, and an unknown third party downstairs had rung both our bells at the same time.

This was how I discovered the doorbell intercom also functions as "bus" where all apartments can talk to each other. (It also blares your conversation onto the street downstrairs, though.)