I love this story! A few years ago I had a server in my apartment with a similar 'dingdong.html' that would ring an old elevator bell I had salvaged from the junk. I didn't end up giving people the URL; I just made an ESP8266 button that would send a request.

If it had been a bit more reliable I would have kept using it but I had some issues with either the bell coil or the relay and it kept sticking. All in all the project ended up being more expensive than a wireless doorbell, but I enjoyed the experience (and the smartwatch notification when someone was at the door).