I Googled “car proximity alarm” and came up with Clifford AdvantGuard 5.5X. There should be more proximity alarms. I encountered one quite a few years ago. When you got within about a foot of the car, a speaker would loudly say “Get away from the car!” or something to that effect.
We have a method to monitor the car that we use away from home once in a while when the occasion demands. We have a dog, kept inside the car, that barks when someone gets too close to our car. I set up an inexpensive FRS radio to VOX (voice activated transmission) and then can hear the dog barking on my receiver in my pocket.