Detect presence of unkown devices (without Wifi)

I have a motion activated mounted tablet in my bathroom and would like to display something based on the condition that I have one or more guests in my apartment.

Since not all of my friends and visitors have access to my wifi, I am looking for alternative methods of detecting the presence of a new mobile device.

Is something like this even possible, perhaps with additional hardware?

Bluetooth / BLE scanning?

You may pickup devices outside the apartment also, perhaps if you see motion and no-one you know is home, is that enough to assume you have a visitor?

This method does not know if the visitor is invited or uninvited though!!

I don’t think you can reliably do this right now without relying on people having certain technology turned on on their device.

This looks very promising, though:

Perhaps someone else already tried to implement something like that.

I guess a way could be to set up motion detectors in your home. To prevent unwanted triggers, you can work with input_boolean and set conditions to check for it’s state.
I did something similar due to family member’s phones sometimes disconect from wifi long enough to trigger ‘away’ - which on re-connect triggered my lights to turn on when they ‘arrived home’, when actualy everyone was sleeping deeply. So I set a boolean to assume, if they were home at bed time, they also are when they seem to ‘come home at 2 am’.

Now how exactly you need to set up your automations depends on what exactly you want to do. I.e if you want lights to turn on when motion is detected but noone is home, you don’t need a boolean.