Answer Description
A mantrap is a buffer area between an unsecured and secured area. Most commonly it is a small room with two doors, each door can only open when the other is shut. Mantraps provide an additional layer of security by reducing tailgating, piggybacking, providing privacy for access measures like a pin number, and in extreme cases trapping potential intruders.
Wikipedia
A mantrap, air lock, sally port or access control vestibule is a physical security access control system comprising a small space with two sets of interlocking doors, such that the first set of doors must close before the second set opens Airlocks have a very similar design, allowing free ingress and egress while also restricting airflow In a manual mantrap, a guard locks and unlocks each door in sequence An intercom and/or video camera are often used to allow the guard to control the trap from a remote location In an automatic mantrap, identification may be required for each door, sometimes even different measures for each door
Mantrap_(access_control) - Wikipedia, the free encyclopedia