

My router (FRITZ!Box) provides entities for all network devices, whether they are currently connected to the network or not.
I trigger all my stuff on when my phone connects/disconnects to my home WiFi. For me this is the best, simplest and least error prone way.
For your use case this would mean needing to have WiFi reception outside your house / in front of your garage, and having your phone reliably and quickly connect to the WiFi when you get home, which might not work great, depending on the strength of your WiFi outside your house.

That sounds like you had your Home Assistant person entity tied to your computers too. If you just go off of your phone’s presence, your laptop or desktop really shouldn’t have any effect on that.