Questions About Doors

I was reading someone's profile on Mibba yesterday (http://member.mibba.com/49578/) and she was all: automatic doors make me feel like a Jedi. And my first thought was: THATS SO TRUE! (:

Strange. I know. But I'm sitting here listening to Stephen Jerzak cover Taylor Swift's White Horse, and I'm seriously thinking about automatic doors. Hahaha.
I mean come on. How do they just KNOW when you're standing in front of the door?
I get the whole motion sensor thing, but do the doors open when snow is falling? No. They don't. Soooo, how does that work?

This is like: how do you lock a revolving door. I really want to know. And how do you get out after you lock it? And why have I never gotten to use one? And why don't stores here have them? I mean, New York has them. Is Virginia not as worthy of revolving doors as NY?

I'm done now.
Thank you for reading.
Good Bye.