Access Control

What Is Access Control?

Access control is the ability to permit or deny the use of a particular resource by a particular entity.

Access control mechanisms can be used in managing physical resources (such as a movie theatre, to which only ticket holders should be admitted), logical resources (a bank account, with a limited number of people authorized to make a withdrawal), or digital resources (for example, a private text document on a computer, which only certain
users should be able to read).

Access control system components

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 electronic lock. In larger applications involving more than one door electric strikes or magnetic locks are used. 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, it could be a card reader, or it could be 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 is used. In concept the door switch is not unlike those on refrigerators or car doors. 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 pushbutton
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. In cases where the lock must be electrically unlocked on exit, the request-to-exit device also unlocks the door.