I have one of those newer intercoms, where you first select who to call, and then it calls the correct flat. So your system wouldn't work. But you just gave me

I have one of those newer intercoms, where you first select who to call, and then it calls the correct flat. So your system wouldn't work. But you just gave me an idea for something I'll probably never implement: an audio key. The intercom auto-responds and if the audio matches the key (hello 90s modem sounds), then it lets you in. You could add more automation on top and provide temporary keys for guests, etc. Just play the audio you received on whatsapp, it will open the door. Please someone implement this and get rich doing it so that I can just buy it. It needs to take into account when you're at home and you still want to answer the mailman.