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Anti-Passback Feature in Access Control Systems

The anti-passback feature is designed to prevent misuse of the access control system. The anti-passback feature establishes a specific sequence in which access cards must be used in order for the system to grant access.


The anti-passback feature is most commonly used at parking gates, where there is both an “in” reader at the entry gate and an “out” reader at the exit gate. The anti-passback feature requires that for every use of a card at the “in” reader, there be a corresponding use at the “out” reader before the card can be used at the “in” reader again. For the typical user of the parking lot, this works fine, because the user would normally swipe their card at the “in” reader to get into the lot in the morning, and swipe it at the “out” reader to get out of the lot in the evening. So long as the sequence is “in – out – in – out – in – out”, everything works fine.


However, if a user swipes his card at the “in” reader to get in, and then passes his card back to a friend, the card would not work the second time when it was swiped by the friend. The attempt to use the card a second time would create an “in – in” sequence that is a violation of the anti-passback rules, and this is why access would be denied.


Anti-passback can also be used at employee entrance doors. This requires that a card reader be installed on both the inside and the outside of the door. Employees are required to both "card-in" when they enter the building and "card-out" when they leave the building. The anti-passback feature is also commonly used with turnstiles.


There is an expanded version of the anti-passback feature called “regional anti-passback”. This establishes an additional set of rules for card readers inside of the building itself. Basically, this rule says that unless a card is first used at an “in” reader at the building exterior, it cannot be used at any reader within the interior of the building. The theory is that, if a person did not enter through an approved building entrance, he or she should not be permitted to use any of the readers within the building.


Depending on the access control system manufacturer, there may be additional anti-passback features in the system. Some of these features could include "timed anti-passback", which requires that a designated amount time pass before an access card can be used at the same reader again, and "nested anti-passback" which requires that readers be used in only designated sequence to enter or leave a highly-secured area.


Denying access when a user attempts to use a card out of sequence is sometimes called "hard" anti-passback. Hard anti-passback means that when a violation of the anti-passback rules occurs, the user will be denied access. Some access control systems also offer a feature known as "soft" anti-passback. When a system is using this option, users who violate anti-passback rules are permitted access, but the incident is reported to the person managing the access control system so that corrective action can be taken - most often notifying the offending employee that the access card should be used in the proper sequence in the future.


The anti-passback feature can also be integrated with the corporate computer system, preventing users from logging on to the network at their desktop computer unless they have properly entered the building using their access card. This feature can also temporarily disable the users remote log-on privileges while the user is in the building - the theory being that if the user is at work, there is no reason for someone from off-site to be logging on to the network using his or her user name and password. When the user leaves the building at the end of the day, his or her remote log-on privileges are turned back on.


(See related Security Tip: The Problem Of "Tailgating")


Have additional questions about the use of the anti-passback feature? Please contact us.

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