I know that in certain countries like Japan or South Korea: it’s normal to leave the front door unlocked since the probaility of someone breaking in is low since their crime rate isn’t high. I knew a friend of mine who resides in Korea where they even left the car unlocked with the keys inside, can you do either of those things in America?
It is highly dependent on where you live. And it’s not density-specific, either. Some cities are sketchier than others. Some rural areas are sketchier than others.
In most cities a block really does make a difference. Where I am I wouldn’t feel afraid if I forgot to lock the door one night. I think it’s weird not to now (having a woman in the house opened my eyes to a lot of new horrors I never once had to worry about).
However, if I went 15 blocks in one direction or another, damn right I’d be sure to turn the car around to make sure I locked the door.