This is a fancy phrase for the locked door, released by a person to grant access to another into the controlled area for authorized personnel. Unfortunately, most access control systems use regular doors with locking devices to control access even though these units are extremely vulnerable to piggybacking, when an authorized cardholder holds open the door for someone they know, and tailgaters, or those who wait for an authorized card holder to open the door and then follow that person into the controlled area. Both piggybacking and tailgaters can compromise the integrity of a controlled environment.
Hence, we are always looking for something in the access control environment that will allow security to check every person, while at the same time be somewhat convenient to the employees, visitors, etc., who are required to use it.
One of the best devices that ensure system integrity by allowing only one person through at a time is the revolving door, but it may not always be the best choice of equipment for high-visibility applications that also require aesthetic compliance. Revolving doors can be very attractive, but work better in most instances for a perimeter application as opposed to an interior one. This led to the development of the optical turnstile.