Hi Sven.
I am also working on making presence detection working, here is what I know so far.
Forget WiFi, iPhones have a habit of turning WiFi off when sleeping and so on.
Bluetooth might be a better option, depending on the size of your home. I have tried to get this working, but haven’t been too succesfull in the use of some scripts I found. However I am able to ping and find the phone, just haven’t turned it into a script.
The best option I have seen so far is to use the “find my iPhone” feature from iCloud. I haven’t tried this yet but take a look here on the forum and this bridge/script 