Also calledEntry controlGate controlZone access
Categories, not lists
Access is granted to a badge category — visitor, exhibitor, contractor, press, VIP — not to individuals. Categories carry rules about which zones and which hours they cover, which is what makes build-up access and trade-only mornings enforceable at a scanner.
Re-entry and its edge cases
People leave for lunch and come back. Re-entry has to be allowed without letting one badge admit three people, which means the scanner tracks direction and the system knows whether a badge is currently inside. That same state is what gives you an honest live occupancy figure.
Capacity by hall
Fire capacity is per space, not per event. Counting in and out by hall gives the operations team a live number against the limit, with a warning before a steward has to turn people away at the door.