First we need a barrier to prevent someone from entering or exiting, such as a locked door or gate. Next we need a way to determine who is trying to enter. A credential reader is used to read the information on a key or card, to register a combination of numbers entered on a pad or to identify some characteristic that the user has, such as a fingerprint the shape of a hand, a pattern in the eye, etc. This identifier is sent to a controller that has stored a record of those identifiers that are authorized to enter the area. If the credential holder is authorized the controller unlocks the gate or door and the credential holder is allowed to enter. In many systems a record of all authorized and unauthorized credentials is stored in the system for future reference.