Which of the following is an example of a passive barrier system?

A passive barrier system is designed to impede unauthorized access without relying on active measures or personnel for enforcement. Closed gates serve as a physical obstruction that prevents entry to a secured area, making them a classic example of a passive security measure. They function effectively to deter potential intruders simply through their presence and physical structure.

In contrast, active security measures, such as security guards, card readers, and alarm systems, require human involvement or electronic systems to function. Security guards actively monitor and intervene in security situations, card readers necessitate user interaction to grant or deny access, and alarm systems respond to detected breaches by alerting relevant parties or triggering alarms. While all contribute to overall security, they do not embody the characteristics of a passive barrier system.