Intrusion
Detection AlarmsThere are two kinds of intrusion detection systems--point protection and space protection. Point protection works for areas such as windows and doors, whereas space protection devices detect movement within an area. Most of your standard house alarm systems (e.g., Brinks, Guardian) use point protection at entry points. A contact-switch set is attached to the window frame and window itself, for example. One side has a magnet that keeps the two switch points apart. When the window is opened, the magnet can no longer hold the spring-loaded contact to prevent the switch from engaging, and the alarm sounds.
This type of system is quite popular; however, it has a major flaw in that it can be defeated by using another magnet to hold the switch contact (though bad guys usually aren't smart enough to know this). Your best solution is to ask your alarm provider to install concealed switches. It will cost more; it will be worth it.
You also have seen glass-break sensors attached to store windows. These are shock or seismic detectors that provide protection for the specific object upon which they are mounted. A fourth type of sensor is the pressure detector. This is a doormat installed under the carpet inside the doorway. An individual's weight on the mat brings electrical contacts together and activates the alarm.
Finally, the last type uses a beam of light shining across the inside of a door or window to a photoelectric sensor. The alarm is activated by interruption of the beam. Today's sensors are infrared light, which is invisible to the human eye.
Those are the types of point protection devices. In our next space protection, and then we'll spend some time talking about how alarms are reported and the goods and bads thereof.
