Between unsecured and secured areas, what term can be defined as a buffer area?

Between an unsecured and secured area, a mantrap is a buffer area. It is most typically a tiny chamber with two doors, each of which can only be opened while the other is closed. Mantraps give another degree of protection by minimizing tailgating and piggybacking, ensuring privacy for access measures such as a pin number, and, in extreme cases, trapping potential intruders.