220-1102 Security Practice Question
A company wants to prevent unauthorized individuals from entering the server room by following closely behind an authorized employee. Which of the following physical security controls would be MOST effective at preventing this type of breach?
⚠ Common exam trap
It's easy for candidates to confuse a mantrap with a simple turnstile or think a key card reader alone prevents tailgating, but the exam tests the specific mechanism of physical interlocking doors that enforce one-person-at-a-time entry.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A mantrap.
A mantrap is a physical security control consisting of two interlocking doors with a small vestibule between them. It prevents tailgating by ensuring only one person can enter at a time; the first door must close and lock before the second door can open, trapping unauthorized individuals who attempt to follow closely behind an authorized employee.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A mantrap.
Why this is correct
A mantrap is an access control vestibule with two interlocking doors where only one door can be opened at a time, creating a small holding area that physically isolates an individual. This design prevents tailgating because the outer door must close and lock before the inner door can unlock, forcing one-person-at-a-time entry and trapping unauthorized individuals inside. It directly mitigates piggybacking by removing any gap for a second person to slip through, unlike passive or observational controls.
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A surveillance camera.
Why it's wrong here
Cameras provide after-the-fact forensic evidence by recording who entered, but they have no active enforcement mechanism to stop a person from following an authorized user through a secured door. In real time, a camera does not trigger a physical barrier or alert, so tailgating can still occur completely unhindered; it only aids investigation of an incident after it happens. Its role is deterrent and evidentiary, not preventative access control.
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A key card reader.
Why it's wrong here
A key card reader authenticates the credential presented by a single user, but it does not verify how many people pass through the door once it is unlocked. Since the door typically remains open for a few seconds after a valid badge swipe, an unauthorized person can simply walk in behind the legitimate user before the door relocks—known as tailgating or piggybacking. The reader authorizes the card, not the physical person, and provides no presence detection for additional entrants.
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A sign-in log.
Why it's wrong here
A sign-in log is a procedural control that relies entirely on the honesty and compliance of individuals to record their entry and exit, with no physical enforcement mechanism to prevent an unauthorized person from simply walking in. It does not require identity verification, does not correlate with door locking, and cannot stop someone who ignores the log or slips in with a group. At best, it creates an audit trail after the fact, but it offers zero real-time resistance to tailgating.
Go deeper
Related to this question
Learn chapter
Physical Security: Locks, Cameras, Access Badges
Key term
Tailgating
Tailgating is a physical security breach where an unauthorized person follows an authorized person into a restricted area without proper authentication.
Key term
Security
Security in IT is the practice of protecting systems, networks, and data from unauthorized access, damage, or theft.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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