In physical security, access control refers to the practice of restricting entrance to a property, a building, or a room to authorized persons. Physical access control can be achieved by a human (a guard, bouncer, or receptionist), through mechanical means such as locks and keys, or through technological methods such as access control systems like the access control vestibule.
Physical access control is a matter of who, where, and when. An access control system determines who is allowed to enter or exit, where they are allowed to exit or enter, and when they are allowed to enter or exit. Traditionally, access was restricted through keys and locks. However, mechanical locks and keys do not restrict the key holder to entry at specific times or dates or record the key used on any specific door. Additionally, keys can be easily duplicated or transferred to an unauthorized person. When a mechanical key is lost or the key holder is no longer authorized to use the protected area, the locks must be rekeyed.