Well.
At night, when living with my parents, I would make sure the doors were all locked. I have always had nightmares about people breaking in.
When I was ~6, there was a window in my room that I couldn’t see from my bed. The fact that I couldn’t see it (and thus, could not tell what was happening) was probably where it all started. Because that was where the point of entry always was in my nightmares there.
When we lived in a suburban area of CA, I would walk around every night and make sure every door was locked. We had an alarm system, but because my sister was a rebellious teen who went out almost every night, we couldn’t use it.
We moved to a rural area (<400 people per square mile). I went around every night double-checking every door and window, and the alarm system. If I didn’t, I would lie awake in bed for hours.
During the daytime when I was a kid, I didn’t worry about the doors being locked. We had 5 people in the house, and we had close neighborhood where everybody knew everybody. A robber would get recognized pretty quickly.
When I was a teen and living in the rural area, it was just 3 of us, with neighbors far away. If my parents were gone, I would immediately lock the doors. If they were home, I would lock the doors ~50% of the time. I mostly did this because I would have loud music on and have tunnel-vision on a computer screen. I didn’t want any surprises.
Now, I’m living with 3 other guys. 2 of the guys have their computers downstairs, they’re always aware of anybody coming/leaving. We have 2 doors, just the front and garage. When I leave the house, I make sure the front is locked and the garage is closed. But if we’re all home, I don’t pay attention to it.
I have never left my car doors unlocked, nor the windows down. I drive a ‘97 minivan with nothing in it to steal. But I’m still worried about it being stolen.
I’m incredibly distrusting and afraid of people in general, though.