Access Control Systems


In the fields of physical security and information security, access control is the selective restriction of access to a place or other resource. The act of accessing may mean consuming, entering, or using. Permission to access a resource is called authorization. Locks and login credentials are two analogous mechanisms of access control.

Physical Security

Geographical access control may be enforced by personnel (e.g., border guard, bouncer, ticket checker), or with a device such as a turnstile. There may be fences to avoid circumventing this access control. An alternative of access control in the strict sense (physically controlling access itself) is a system of checking authorized presence, e.g. Ticket controller (transportation). A variant is exit control, e.g. of a shop (checkout) or a country.The term 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 means such as access control systems like the mantrap. Within these environments, physical key management may also be employed as a means of further managing and monitoring access to mechanically keyed areas or access to certain small assets.

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. Historically, this was partially accomplished through keys and locks. When a door is locked, only someone with a key can enter through the door. Mechanical locks and keys do not allow restriction of the key holder to specific times or dates and 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 this key is lost or the key holder is no longer authorized to use the protected area, then 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. This 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

Access control system operation

When a credential is presented to a reader, the reader sends the credential’s information, usually a number, to a control panel, a highly reliable processor. The control panel compares the credential’s number to an access control list, grants or denies the presented request, and sends a transaction log to a database. When access is denied based on the access control list, the door remains locked. If there is a match between the credential and the access control list, the control panel operates a relay that in turn unlocks the door. The control panel also ignores a door open signal to prevent an alarm. Often the reader provides feedback, such as a flashing red LED for an access denied and a flashing green LED for an access granted.

There are three factors of authenticating information:-

  • Something the user knows, e.g. a password, PIN.
  • Something the user has, e.g. smart card or a key fob.
  • Something the user is, e.g. fingerprint, verified by biometric measurement.

Passwords are a common means of verifying a user’s identity before access is given to information systems. In addition, a fourth factor of authentication is now recognized as someone you know, whereby another person who knows you can provide a human element of authentication. For example, a user may have their password, but have forgotten their smart card. In such a scenario, if the user is known to designated cohorts, the cohorts may provide their smart card and password.


A credential is a physical/tangible object, a piece of knowledge, or a facet of a person’s physical being, that enables an individual access to a given physical facility or computer-based information system. Typically, credentials can be something a person knows (such as a number or PIN), something they have like an access badge, something they are (such as a biometric feature) or some combination of these items. This is known as multi-factor authentication. The typical credential is an access card or key-fob, and newer software can also turn users’ smartphones into access devices.

There are many card technologies including magnetic stripe, bar code, card-swipe, contact smart cards, and contactless smart cards. Also available are key-fobs, which are more compact than ID cards, and attach to a key ring. Biometric technologies include fingerprint, facial recognition, iris recognition, retinal scan, voice, and hand geometry. There are newer technologies such as Near field communication (NFC) and Bluetooth low energy also have potential to communicate user credentials to readers for system or building access.

Access control system components

An access control point can be a door, turnstile, parking gate, elevator, or other physical barrier, where granting access can be electronically controlled. Typically, the access point is a door. An electronic access control door can contain several elements. At its most basic, there is a stand-alone electric lock. The lock is unlocked by an operator with a switch. To automate this, operator intervention is replaced by a reader. The reader could be a keypad where a code is entered, card reader, or a biometric reader. Readers do not usually make an access decision, but send a card number to an access control panel that verifies the number against an access list.

To monitor the door position a magnetic door switch can be used. Generally only entry is controlled, and exit is uncontrolled. In cases where exit is also controlled, a second reader is used on the opposite side of the door. In cases where exit is not controlled, free exit, a device called a request-to-exit (REX) is used. Request-to-exit devices can be a push-button or a motion detector. When the button is pushed, or the motion detector detects motion at the door, the door alarm is temporarily ignored while the door is opened.

Exiting a door without having to electrically unlock the door is called mechanical free egress. This is an important safety feature.Access control decisions are made by comparing the credential to an access control list. This look-up can be done by a host or server, by an access control panel, or by a reader.

Computer Security

In computer security , general access control includes authorization, authentication, access approval, and audit. The system makes a decision to grant or reject an access request from an already authenticated subject, based on what the subject is authorized to access. Authentication and access control are often combined into a single operation, so that access is approved based on successful authentication. Authentication methods and tokens include passwords, biometric scans, physical keys, electronic keys and devices, hidden paths, social barriers, and monitoring by humans and automated systems.