General Access Control is designed to restrict access to specific resources by specific entities. Meanwhile, in building security management, an Access Control System (ACS) is designed to restrict access to a specific area or room to a specific person or persons. It determines the persons who are able to enter a particular space or open a particular door at a particular time. The system achieves this by using a combination of electric and electronic components. An ideal ACS has several components (i.e., electric lock, reader, emergency exit device, uninterruptible power supply, and controller board).

Architecturally, ACS can be divided into two types: stand-alone systems and network-based systems. A stand-alone system combines the reader and controller board into one device; a network-based system separates the reader and controller board. By separating the reader and controller, a network-based system is more secure. The controller in a network-based system also has more expandable capacity as it can be linked to control several doors.

An electric lock is used to bind the leaf door and its frame. The function is similar to a traditional mechanical lock; the difference is in the lock control mechanism. Unlike traditional locks, which uses a key to open the lock, an electric lock uses electric current. There are a variety of electric locks according to the type of door and weight of the door. Based on the type of door, there are three types of electric lock: electric door strike, electromagnetic lock, and drop bolt. Each type of lock has its own advantages and disadvantages to meet specific technical requirements and cost limitations.

A reader is used to identify the person entering the protected area or room. The input received by the reader to identify the person can be a card, pin, or biometric image. After identifying the person, the reader sends the identity to the controller. Communication between reader and controller is established by using a standardized protocol such as the Wiegand format.

The most important component of an ACS is the controller board. The controller board stores all the logic and user databases. After receiving the identity of the user from the reader, the controller checks the privilege of the user in its access control database; it then takes appropriate action (e.g., opening or closing the electric lock). The controller board also manages communication with the ACS. Communication with the server is necessary to maintain the consistency of data. The controller board downloads the configuration and user database from or to the server and synchronizes the differences.

The last component in an ACS is an emergency exit device. The device is used to open a lock without inputting an authorized identity through the reader. Although the devices are not compulsory, it is crucial for operational continuity. Several devices commonly used to trigger an emergency exit are an exit button, breaking glass, and a key switch. An exit button and breaking glass open the lock from inside a protected area, while a key switch opens the lock from outside.