In inner city Baltimore, we always kept all the doors locked, for obvious reasons.
Our car was broken into twice - once I think a homeless person just spent the night inside and drained the battery, and the second time they just stole our GPS unit.
Since moving here, I haven't been as strict about locking my car. I always do at the store, in places where there are lots of people, etc. Not always at home. I know, that sounds really dumb.
I just heard there has been an increase in car break-ins in the area; specifically, windows being smashed in.
In Baltimore, I rarely, if ever, saw a window broken in. I know it happened, I just didn't see it in the places I lived. Thieves were relying on unlocked cars and easy-to-unlock cars.
It sounds like here, if someone is going to break into my car, they are going to break into my car regardless of whether it is unlocked or not. So, my thinking is that I might as well leave the door unlocked to prevent further damage. My stereo is not worth stealing; the only thing worth stealing is the car seat, which costs less than the deductible I'd have to pay if someone caused any damage, theft or otherwise, to my car. Also, funny as it may sound, out of all my friends who had their car broken into in Baltimore (all of them), not ONE had a car seat stolen. One just had some charging cords stolen, with 2 brand new car seats sitting in the back seat. Makes me laugh. Kind of.