An access control system is the modern replacement for the old lock-and-key system for gaining entry. With the system in place, you can lock any door so that only those with the proper access control device can pass through. This device can take a number of different forms. It can be a card you swipe or pass over the access reader, it can be a fob that the person wishing to gain entry carries on their person, which is then read by the reader, or it can even be a biometric reader that scans a fingerprint or the retina.