Both doors are locked. Door One goes from an outside area into the mantrap, and Door Two goes from the mantrap into an inside/protected area. In order to enter into the mantrap through Door One, you need to engage the corresponding request-to-unlock contact.

This can be done through the relay output of a card reader, keypad, or a remote switch pressed by a security guard. The same goes to enter the protected area from the mantrap through Door Two. When exiting the protected area, a regular request-to-exit button or passive infrared detector would also work.

This mode would be used in something like a school entry hall, where authorized personnel can enter the outer door by presenting a keycard or code, which activates the request-to-unlock contact. Or a guard can buzz you in by activating a remotely installed button, which is wired to the request-to-unlock contact. While one door is open, the other door is locked to avoid free flow.