It's for everyone. The visible burden can vary greatly, so the only reliable way to keep the crazies out is to check everyone. I'm sure there are some hidden entrances, sympathetic guards, and other exploits in a few SZs though if a Burdened were desperate enough. I am legitimately nocturnal and I only have Tuesdays and Thursdays off, so I apologize if my responses to your questions aren't very fast.