Slightly different take on this, some years ago a good friend had his immaculately restored RS2000 stolen from his locked garage. I should point out that he was the grounds man of a private estate with security gates. He lived in a cottage in the grounds and has three rather loud Jack Russell dogs, but never heard the robbers. The car was always locked even though inside a locked garage and the estate is at least three miles from the nearest decent road.
Fortunately he had an agreed value policy, but even though he had been insured with them for several years, he still had to endure several weeks of enquiries by their claims management company before the insurers finally coughed up.
On a related point, many moons ago a works rally Ford Escort was stolen from parc ferme prior to an International rally by thieves who must have known that all the works cars shared the same keys and that their bespoke parts were all stamped as such and had the wherewithal to transport their prize away quietly under cover.
I guess the message is, if thieves want your car you need to decide how much it’s loss is worth in terms of theft prevention measures?