DoorTek has designed a ManTrap Interlock Hardware system that preserves anti-pass-back. The system places a very nice Interlock Request plate on either side of the ManTrap. The request plate has a Interlock Request Button, a red led that indicates the locked-out status, and a green led that indicates Interlock Request Granted. A cardholder, upon approaching the door, can tell if the door is blocked by the red led. If the door is not blocked, the cardholder presses the Interlock Request button. Upon acceptance of the request the green led will be lit. The cardholder then presents the card to the reader. When the green led is lit  the reader is active and the opposite side is totally blocked. Only once the door is closed and locked will the other side become available for activation.