Turnstile — Entrance [better]

Turnstile entrances offer several benefits, including:

Tailgating (or "piggybacking") is one of the biggest security vulnerabilities in any building. This occurs when an unauthorized person slips in behind an authorized user through an open door. Standard doors cannot prevent this, but a turnstile makes it physically impossible for two people to pass through a single rotation simultaneously. turnstile entrance

The turnstile behind Clara clanked—once, twice. She spun around. A man in a gray uniform stood there, his face kind but firm. “One ticket, one turn,” he said gently. “You can’t stay. The gate only opens one way for each soul.” Turnstile entrances offer several benefits

And then she saw her.