To prevent people who do not have access to the door, walk through. Unable to leave room. Solve the problem other people who are not officials or people walking by to enter the building
To protect people who are not walking through the door to scan. Can not leave the room Help solve a person other than an officer or personnel went to the building.
To the person who does not scan walk through the door, cannot leave the room To solve the other person not officers or personnel went on to enter the building