I’ll reply here also to @ratumoko@kbin.social - the building security is a joke. The company rents some offices in these share-space buildings. And there is no real security beyond that (OK, fine, also some cameras). I suspect that they use this system just to keep costumers happy, feeling like there is some security system in place. I’ll try the RFID ring and see if it works.

But my “real” question here is how come I didn’t find any app/instruction for making my phone itself an RFID keycard. As I type this I realize that this might be due to needing a specific frequency that the phone cannot produce(?)

That’s the technology they use: nfc-tools.github.io/resources/…/iso14443A/