An access control system determines who is allowed to enter or exit, where they are allowed to enter or exit, and when they are allowed to enter or exit. Historically this was partially accomplished through keys and locks. Mechanical locks and keys do not allow restriction of the key holder to specific times or dates & do not provide records of the key used on any specific door and the keys can be easily copied 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 re-keyed.

Electronic access control uses computers to solve the limitations of mechanical locks and keys. A wide range of credentials can be used to replace mechanical keys. The electronic access control system grants access based on the credential presented. When access is granted, the door is unlocked for a predetermined time and the transaction is recorded. When access is refused, the door remains locked and the attempted access is recorded. The system will also monitor the door and alarm if the door is forced open or held open too long after being unlocked.

Components
1) Controller
2) Readers
3) Types of Cards / Methods
There are three types (factors) of authenticating information:

• something the user knows, e.g. a password, pass-phrase or PIN
• something the user has, such as smart card or proximity card
• something the user is, such as fingerprint, verified by biometric measurement