Overview: Physical Security Controls – Part 2

Detective Physical Access Controls

Preventive physical controls are not perfect. Eventually, an intruder will successfully circumvent one or more or them. So let’s look at some of the ways you can implement detective controls to support your perimeter defenses.


Technology can play a large role in detecting whether an intruder has gained access to secure or peripheral areas. Examples include:

  1. Light beams – A person or object moving through an area will break a beam of light passing between an emitter and receiver. When this occurs, an audible or silent alarm is initiated.
  2. Vibration/sound detector – These types of detection devices are often used to detect tampering with windows, doors, gates, or other barriers to entry. For example, a vibration detector might alarm with the breaking of a window. Mounting detectors to perimeter fencing is a common method for detecting intrusions as soon as someone enters your property.
  3. Motion detector – Motion detectors serve a similar purpose as light beams. People or objects moving through an area are detected and alarms initiated. Motion detectors are a good choice if you need to completely cover an area. Properly implemented, they should provide better overall security than light beam technology.
  4. Closed Circuit TV (CCTV) – This control provides for continuous monitoring of perimeters and sensitive areas. However, it requires security personnel to watch for and react to incidents.


No technology-enabled detective control is effective unless coupled with human intervention. Immediate reaction depends on in-house security personnel. They can quickly assess and react to alarms or visually identified incidents. Whether or not you need your own security staff depends on two things – the level of risk associated with the compromise of your physical controls and the speed with which local law enforcement can respond to alarms.

Fire Detection

Although I’ve separated our review of fire detection controls from that of fire prevention controls (see Part 1), both preventive and detective methods and technologies are required for effective fire prevention and control. There are two primary types of fire detection sensors: smoke and heat. Many "smoke" detectors are designed to detect any unusual gasses that might be caused by fire or heat. I prefer this type. Heat detectors might not initiate an alarm until a fire is well underway.

Detectors should be placed under your data center’s raised floor, in the plenum space above the ceiling, and in air ducts.

This post is part of the series: Overview of Physical Security

This is a series of two articles discussing the purpose of physical security, common controls, and how to implement them.
  1. Physical Security Controls – Part 1
  2. Physical Security Controls – Part 2