What do you do if you see your neighbors car door left open?

I notice they leave their door open sometimes & I always ask myself if I should knock on the door & tell them in case theres a sensitive car alarm.. or just close it myself & hope there's no alarm so they don't think I'm a criminal 😂

I always just close it myself & luckily there's no alarm. I still think about how awkward it would be to explain if there was though lol