OMIGAWD!
I used to do that. I was totally obsessive about it. I'd check them over and over again, getting up out of bed to check and re-check on them. Windows, doors, the whole 9 yards! When I got together with my now husband, I realized how wierd it was and how disabling it was and have weened myself off it. I still check them once, but that's because they are usually unlocked and there are some WIERD people out there in the neighbourhoods! So, you aren't alone out there... I don't think it's a wierd habit either. I think it is being safe and diligent and conscientious!
Wierd habits for me... hmmm... there are so many!!!
I can't have anyone touching me when I'm sleeping. Not event a big toe. I sleep in a little cocoon, with the sheets almost wrapped around me, my arms pulled in close. But I can't 'snuggle' to sleep like the average person. I have to, as I always say to my husband, 'sleep independently.' He hates it. But I think it's a rather wierd habit.
What else? Oh so many things. If I list them all, you'll all think I'm psycho. And I'm not. Just a little obsessive compulsive!