Which of the following is a physical perimeter security control?

Surveillance systems are considered a physical perimeter security control because they involve the use of physical devices to monitor and protect the boundaries of a facility. These systems can include cameras, motion detectors, and access control systems that help ensure that unauthorized individuals do not breach the physical perimeter of a space. The primary function of surveillance systems is to provide visibility and deter potential threats, making them integral to a comprehensive security strategy.

The other options are focused on digital security measures rather than physical security. Firewalls protect networks by filtering incoming and outgoing traffic, encryption systems protect data by converting it into a secure format, and antivirus software safeguards computers from malware and other cyber threats. While all these tools are crucial for overall security, they do not address the physical aspects of security like surveillance systems do.