OVERVIEW
Physical security is primarily concerned with restricting physical access by unauthorized people (commonly interpreted as intruders) to controlled facilities, although there are other considerations and situations in which physical security measures are valuable (for example, limiting access within a facility and/or to specific assets and controls to reduce physical incidents such as fires).
Security unavoidably incurs costs and, in reality, it can never be perfect or complete - in other words, security can reduce but cannot entirely eliminate risks. Given that controls are imperfect, strong physical security applies using appropriate combinations of overlapping and complementary controls. For instance, physical access controls for protected facilities are generally intended to:
• deter potential intruders (e.g. warning signs and perimeter markings);
• distinguish authorized from unauthorized people (e.g. using pass cards/badges and keys)
• delay and ideally prevent intrusion attempts (e.g. strong walls, door locks and safes);
• detect intrusions and monitor/record intruders (e.g. intruder alarms and CCTV systems); and
• trigger appropriate incident responses (e.g. by security guards and police).
It is up to security designers to balance security controls against risks, taking into account the costs of specifying, developing, testing, implementing, using, managing, monitoring and maintaining the controls.
Physical access control is a matter of who, where, and when. An access control system determines who is allowed to enter or exit, where they are allowed to exit or enter, and when they are allowed to enter or exit. Historically this was partially accomplished through keys and locks. When a door is locked only someone with a key can enter through the door depending on how the lock is configured. Mechanical locks and keys do not allow restriction of