Key Objectives of Perimeter Security

Outdoor perimeter security is an often-overlooked area of physical security design that can dramatically improve the effectiveness of a facility’s security system. If you are involved in designing or managing physical security the infrastructure located in the buildings likely consumes the majority of your budget. However, small investments in outdoor perimeters can provide significant protection to the building’s assets well before the other, more costly, measures are encountered. These outdoor perimeters can serve as a valuable line of defense for a physical security plan because they add distance, time and scale to a physical security plan that cannot be achieved within the building itself.  If designed correctly, outdoor preventative measures can reduce the cost of building security. In all physical security designs outdoor perimeters should be included as a supportive element.

To correctly utilize the outdoor perimeter requires that the security plan take a holistic and complete assessment of the outdoor and indoor areas. A holistic perimeter reference design is the 5D’s of perimeter security. This design focuses on a key objective for each specific perimeter, and layers the perimeters from outside the facility to inside the secured buildings. The 5D’s starting from the outside are: Deter, Detect, Deny, Delay and Defend. 


The deter perimeter is the farthest one from the location of the assets and is often a mix of physical infrastructure such as fences and lighting. The security objective on this perimeter is to deter the criminal from even attempting a breach of the system. Deterrence is a psychological battle, and when the security department wins, the criminal activity never starts. Applying surveillance technology along the deter perimeter typically requires the use of overt, large enclosures, which make it obvious to all approaching the perimeter that they are under surveillance. Signs saying “no trespassing” or “area under surveillance” also aid in communicating a deterrent message to unauthorized persons.


The detection perimeter’s security objective is to monitor large areas of space to accurately detect possible unauthorized intrusion in time to respond appropriately. Surveillance camera technology, especially megapixel cameras, is very effective as an accurate detection tool. Important objectives are the timely notification to security personnel, and having the ability to digitally or optically zoom into the area where intrusion was detected.


The objective at the deny perimeter is to keep unauthorized persons out, while allowing authorized persons to enter. To perform this function the deny perimeter typically has access control technology or a manned security gate at the point of entry. The intention of surveillance at this point is to provide visual verification to the biometric or card access system.


The delay perimeter’s objective is to slow down an active intrusion enough to force the intruder to give up, or allow the security team to respond. Often, interior locking doors or other physical barriers are used to slow down the intrusion. Surveillance cameras can be used inside the delay perimeter to provide situational awareness and measure the effectiveness of the delay countermeasures.


The defend perimeter is typically a security personnel response that attempts to apprehend the intruder.  Surveillance is used at this perimeter to record the apprehension and determine the effectiveness of the response.  This final perimeter often includes the involvement of law enforcement and typically overlaps the other perimeters.

Keys to Outdoor Perimeters

The general rule is that the farther away from a secured building the more expensive are the security measures. This holds true for cameras, sensors and access control systems. Designing outdoor systems requires detailed upfront planning because of the wide range of operating conditions to which the security systems will be exposed. For cameras, lighting and weather conditions are the biggest problems the system will have to overcome through infrared light and motion sensors. Holistic design processes that combine both indoor and outdoor perimeters, similar to the 5D’s, will provide the most effective physical security systems.   

Marier, Keven. (2012). “The 5 D’s of Outdoor Perimeter Security”. Retrieved from