More than a few seconds, and the thieves are looking for convenience and speed. There are lots of with cats they could take. If they look under a car and see a shield, they’re going to find another car that’s easier to remove and doesn’t leave them in a vulnerable position doing something loud and obviously illegal for any longer than they have to. If someone was really committed to getting your exact cat they will get it shield or not, but most thieves are risk averse and would rather just try a different car