Intrusion Detection Techniques & Approaches

Boundary Penetration

• Boundary penetration is an intrusion-detection technique that makes use of virtual borders around a protected area. When this technique is used, an alarm is activated if an intruder crosses a preset border or line. Commonly, this border is a natural entry point such as a doorway or window. This technique can also be applied to other boundaries, such the outer perimeter of a room.

  Several different sensors can be used to apply this detection technique. A glass-break sensor, for example, can be placed on the windows of a home or business. These sensors are tuned to detected the high-frequency sound created when glass shatters. If a perpetrator attempts to pass through the boundary by breaking the window, the sensor activates and an alarm sounds.

  Another commonly used type of boundary penetration sensor is the magnetic switch. This sensor consists of a magnet, which is mounted on a door, and a magnetic switch placed in the door frame. When the door is closed, the magnet keeps the magnetic switch closed. If the door is forced open, however, the magnet is pushed away, and the circuit is broken. This signals that the boundary has been penetrated, setting of an alarm.

Interior Motion

• A second type of intrusion detection is called the interior motion technique. This method is used to detect intruders after they have penetrated the outermost perimeter, but before they are able to reach a protected area. In a business example, sensors placed in the lobby of a bank would be considered interior motion detectors, because they indicate that somebody is already in the building but not yet at the protected asset, such as a vault.

  One of the most common types of sensor used for the interior motion technique is called a Passive Infrared Sensor (PIR). These devices detect infrared heat energy, such as the body heat of a person. PIR sensors are tuned to send a signal in the event of fast-moving heat changes. This way, a gradual temperature increase caused by heating ducts will not set of the alarm, but the heat from a perpetrator walking past will. Passive infrared motion detectors are common in both homes and businesses.

  Video Motion Detection (VMD) is another commonly used technology for interior motion detection. Like PIRs, video motion detectors look for rapid movement in an area. Instead of seeing body heat, however, VMDs compare changes in an image captured from a camera. If a large change in the picture occurs, such as when a person walks past the camera, an alert signal is sent.

Proximity

• The third type of intrusion detection is known as the proximity technique. While the previous two techniques focus on detecting an intruder before he reaches a protected area, the proximity method sets off an alarm when the perpetrator comes near the actual safeguarded item. In the bank example, a proximity detector would sound an alarm if a thief approached the door of the safe.

  One common proximity detection technology is the proximity pressure sensor. This type of sensor can be placed in the floor around a protected asset and detects changes in pressure caused when somebody steps onto the surface. To continue the bank example, the floor of a vault might have a proximity pressure sensor installed. This would activate an alarm the moment a thief came close to the stored money.

  While the proximity detection technique can be used by itself, it is most commonly used as a last resort in conjunction with other sensors. The most secure facilities combine all three of the previously mentioned techniques, forming three distinct layers of protection.