How to make my intercom smart?

Hi all,

Im wondering if someone can help me out with the last steps to make my old apartment intercom smart. My apartment has an “Siedle HT-511 01” intercom system (see attached pictures)

Im trying to make the system smart with a Shelly Uni or Shelly one. The system get 11V AC when the doorbell rings. The only challenge I have is that there is no external power possibility around.

I figured out the cable installation already, which should be:

-C an I to “measure doorbell ring”
-C and 7 to “buzzer door”

Is there any one that could possibly help me out here with knowing if its possible to connect a Shelly one to the existing power supply / cabling. If yes, which cables could it be?

Would love to hear your thoughts.
If there are any other suggestions, please feel free to share. Looking for the best suitable solution here.