Presence Detection with keyring for AirBnB?

Hello everyone!

I own a small apartment that I am renting through AirBnB. I am looking for ways to reduce power consumption and emissions. I am looking for a system that works by itself, meaning that it does not need any specific actions from the users.

I was thinking of adding a conventional card key system like in hotels, but that requires a lot of work setting up the electrical side of it. My house is brick and mortar and it will require a lot of digging on the wall to get the cables through.

So, I stumbled upon the Shelly EM, which will be perfect for me since it can drive a contactor to conect/disconnect electrical networks to the main feed, as well as let me track energy usage.

My question is, how can I implement presence detection on the key?