🚀 go-pugleaf

Your problem is a very common one with radio communications.
Most large buildings (shopping centers being generaly the worst) just seem
to stop dead almost all radio communications.

I have had similar experiences with ham radio equipment, in one case
a local repeater (less than a mile away, running 25 watts) just vanished
upon entering a department store.

I really don't see much hope for your system working in such circumstances.

You can probably console yourself with the fact that even if you get
your warning while more than a few hundred feet away from the car, by
the time you get there either the car or its contents will be long gone.

Philip