wat la you, if the guard stopped your relative from coming in, they got blamed, now they let outsider in, also got blamed as well. seriously if you cant trust the guards, then install good quality CCTV and make sure the viewing angle is good enuff to identify every person on the car.

and btw, if the thief able to get pass the security of the car, i bet if they want, they should be able to make the tag to get in as well.