Page154

Contraband Checks

Anyone traveling through airports is familiar with contraband checks, which seek to identify objects that are prohibited to enter a secure perimeter (such as an airplane). Secure buildings such as government or military buildings may also employ contraband checks.

These checks are often used to detect metals, weapons, or explosives. They may also be used to detect controlled substances such as illegal drugs. Another concern is portable cameras or storage media that may be used to exfiltrate sensitive data.

Defense-in-depth strategies such as port blocking should be used in addition to contraband checks that seek to detect contraband such as portable media. For example, a “microSD” (micro Secure Digital) card used in some digital cameras can store multiple gigabytes of data and is smaller than a penny: small enough to evade all but the most thorough contraband checks.

Motion Detectors and Other Perimeter Alarms

Ultrasonic and microwave motion detectors work like “Doppler radar” used to predict the weather. A wave of energy is sent out, and the “echo” is returned when it bounces off an object. A motion detector that is 20 feet away from a wall will consistently receive an echo in the time it takes for the wave to hit the wall and bounce back to the receiver, for example. The echo will be returned more quickly when a new object (such as a person walking in range of the sensor) reflects the wave.

A photoelectric motion sensor sends a beam of light across a monitored space to a photoelectric sensor. The sensor alerts when the light beam is broken.

Ultrasonic, microwave, and infrared motion sensors are active sensors, which means they actively send energy. A passive sensor can be thought of as a “read-only” device. An example is a passive infrared (PIR) sensor, which detects infrared energy created by body heat.

Exam Warning We often think of technical controls like NIDS (Network Intrusion Detection Systems) when we hear the term “intrusion.” Motion detectors provide physical intrusion detection.

It is important to remember that the original intrusions were committed by human “intruders” (who may have stormed a castle wall). If you see the term “intrusion” on the exam, be sure to look for the context (human or network-based).

Perimeter alarms include magnetic door and window alarms. They include matched pairs of sensors on the wall, as well as window/door. An electrical circuit flows through the sensor pairs as long as the door or window is closed; the circuit breaks when either is opened. These are often armed for secured areas as well as in general areas during off hours such as nights or weekends. Once armed, a central alarm system will alert when any door or window is opened.