What is defense-in-depth and why is it used in facility security?

• A. A single, strong lock guarding a single entry.
• B. A layered security approach using multiple controls to reduce risk and provide redundancy.
• C. An approach that relies solely on surveillance cameras.
• D. A defensive posture focusing on external fencing only.

Answer: (B)

Defense-in-depth is a layered security approach that uses multiple controls at different points to reduce risk and provide redundancy. By combining physical barriers (fences, doors, locks), technical measures (card readers, alarms, cameras), and administrative actions (procedures, training, patrols), an organization creates overlapping protections that a would-be intruder must overcome. If one control is bypassed or fails, other layers still stand in the way, slowing entry, increasing detection, and buying time for a response. This approach is used in facility security to protect people and assets even when a single control isn’t perfect.

Why the other ideas don’t fit: relying on a single strong lock focuses on one control and lacks redundancy; cameras alone don’t prevent entry and may not deter someone with access; fencing by itself doesn’t manage interior access or provide timely detection.