I'm somewhat convinced by now that the security system is in some way connected to the elevator system here. I think that when somebody swipes their badge to get in through the front doors, if there are any unused elevators at the time, one returns to the first floor. More than half the time when I enter the building, an elevator immediately opens for me as soon as I round the corner, even though there's no one around who could have pushed the button. It's weird. Convenient, but weird.