$39 will get you this dash cam with motion activated “parked” mode. I have no idea about the quality of the product but if nothing else, it would allow you to put a sign on your car saying “this vehicle is now protected by video surveillance”.
Oh, and before everyone starts jumping up and down about privacy issues, there are none worth bothering about.
That said, you might want to ask your strata committee what they can do. A tyre that bursts causing an accident because the garage isn’t as secure as it should be could become an issue for them. A letter to all residents asking them to report suspicious behaviour might scare off your saboteurs.