Some years ago I had an older analog intercom and added some intelligence for the open button, ignoring the audio part. Doing it with an ESP01 was trivial and I only needed access to my intercom box inside the apartment. The first issue I ran into was that no matter how much I optimized, the power consumption was high and made the thing semi-useless. Then I got smarter and powered it from the 24V lines coming from the intercom system. That worked great until I realized that where I live this counts as stealing electricity so I scratched that, why take the chance that the building administrator notices something and I get burned.

Eventually I got a Nuki Opener which works with all kinds of intercoms and is way less effort. Janky builds are awesome but better for the playground than as a solution you really want to be reliable for the whole family.

P.S. The code from the article should be linked more prominently [0], for anyone who wants to tinker.

[0] https://github.com/ImTheSquid/doorbell2