With LoJack dead in the US, what is a classic car GPS tracking alternative?

Go buy a burner phone,

Find a out of the way place in the trunk

Tap into a hot wire or run a new one.

Get a low cost cell plan

Download a find my phone app.

Cell phone stays charged and if battery was disconnected will work for a day?

Only issue I can see is if phone battery died and phone needed to reboot.