Which of the following is an example of a passive measure in physical security?

Locked doors are considered a passive measure in physical security because they provide a constant and stationary form of protection that does not require active human intervention or monitoring to maintain their effectiveness. This means that as long as the doors are securely locked, they serve their purpose of restricting access, making it more difficult for unauthorized individuals to enter a secure area.

In contrast, security cameras, security personnel, and alarm systems are active measures that require monitoring, response, or action to ensure the safety of a facility. Security cameras can help in active monitoring and recording events as they occur, while security personnel are typically on-site to respond to potential threats actively. Alarm systems also require an active response when triggered, as they alert monitoring personnel or law enforcement to take action. Therefore, locked doors stand out as a passive measure since their effectiveness relies on their physical barrier without the need for ongoing management.