Access control is simply the action of ensuring that only the correct people are allowed to access certain spaces or assets. Most standalone access control systems are based around doors, which rely on readers that grant or deny access, meaning that they unlock the door. This happens when a cardholder presents a valid badge or other forms of credentials, alerting the reader that a user is requesting entry.
There are a few different types of single-door access control systems commonly used in the industry: keypad-based, card reader enabled, and biometric-based systems are a few of the most popular ones.