Anti-passback is used to prevent one tag user from giving his tag to another user in order to gain access. For anti-passback to operate first you must select the Anti-Passback Control option, and then readers must be set as being In or Out. Passback may be simply monitored (select from the menu when monitoring), or enforced at each reader (in which case access to the door will be barred if a tag is scanned more than once at readers of the same direction).
Each controller will maintain its own list of which users are In and which users are Out, and it will use this list to enforce anti-passback at all times if required to do so. For anti-passback monitoring and control to work across more than one controller Access Manager must be running at all times, as Access Manager is reponsible for transferring the anti-passback information from each controller to the others.
Anti-passback violations can be cleared either by going to a reader of the opposite direction, or by using the button for the user who has broken the anti-passback rule.