Two different ways to physically stop tailgating — not just detect it — and why picking the wrong one for a busy lobby or a data center door is a real design mistake.
"Anti-tailgating" sounds like one feature, but it's really a spectrum. An optical security turnstile watches for a second body following a single valid credential and reacts with sensors and alarms — while still letting a real line of people move through quickly. A mantrap (interlocking vestibule) doesn't watch for tailgating at all; it makes simultaneous dual-door passage mechanically impossible in the first place. Confusing the two — or treating the choice as a matter of budget or looks — is how a data center ends up with insufficient assurance at its most sensitive door, or a busy lobby ends up with a bottleneck it can never move enough people through.