It's amazing how well that works with typical building security (provided there are no physical barriers like locked doors). If you walk into a secure area briskly, like you belong there, the security guards tend to leave you alone. You also have to be well dressed.
When my wife was in the hospital last year, you were supposed to sign in at the front reception area and get a badge. I never did that. I just walked right up to the elevator banks in my business suit and nobody ever challenged me. I guess they figured I was a doctor or some other important person.
Then one time, I show up in casual clothes and I get the "Can I help you sir" treatment before I even get halfway across the atrium and they made me sign in like any other dweeb.