I'm not totally knowledgable about insurance, but I'm pretty sure if you leave the car door unlocked (or apartment door for that matter), insurance doesn't cover the theft. There needs to be some sort of forced entry, as far as I remember.
I left my car unlocked and accidentally left the garage door up. I lost the stereo from the car, and suffered a lot of console damage as well. I had two surfboards, some tools and a set of CD's stolen. It was all completely my fault for bumping the garage door remote (I now leave it in the car, always).
The insurance company paid up, both for the household items taken, and the car insurance for the stolen stereo and damaged interior. In fact, with the new-for-old policy, I got replacements on some old stuff with nice new items.
The takeaway is : check your policy. You want to insure against loss and stupidity.
If you lived in a bad enough neighborhood and had an insurance policy like that, "accidentally" leaving your doors unlocked would be a cheap and easy insurance fraud--which is why some insurers are reluctant to cover people in that situation.
Well I always live in good neighbourhoods, so I guess the insurers don't mind in my case. My current policy also covers theft of items stored outside the house - bikes, ladders, furniture, etc.
Sometimes it's not always cheaper to live in bad areas, when you add up the total cost of living.
