I use my personal phone as a presence sensor to turn on lights when I arrive home and disarm the system. It works great.
For my child, I currently use an old ST arrival
Sensor. It does not work as well. As an alternative, is there a way I can use my child’s iPhone as their presence/arrival sensor, without giving them access to the ST app? If my child has access to the ST app, I fear they will accidentally mess up my routines and other things I have set up in the ST app.
do you have an Apple TV, HomePod mini or always on iPad at home? if yes, you can purchase a homekit version of the Meross outlet (very inexpensive) that can trigger Routines. in homekit, setup a rule that when the iPhone arrives, turn on the meross outlet through homekit, when it turns on, it will trigger the Routine in ST. short version for how to do it.
Do you have a PC that is always on?
In that case you could use @TAustin 's bridge and presence app. Mine works almost flawless, sometimes I get a drop occasionally, but adding a delay to things happening when leaving is not an issue for me, so I give it a minute to turn off all lights.
I recall some issues with apple though, so need to test a bit.
People have been asking for this ability in ST FOREVER! It ain’t happening. The best workaround was using Life360, but ST has torched that. Presence sensing, a pretty basic function for a smart home platform is a complete mess in this ecosystem now. Good luck