Basic Principles of Burglar Alarm Systems.

In this introductory chapter we are going to look at the basic building blocks of alarm systems. In later chapters we will look in more detail at these devices, how they work, how they are wired and how they are used in designing systems. For the moment, however, let us concentrate on the basics.

All alarms system consist of four main component areas:

1. Detection Devices, to detect if an intrusion has occurred
2. Warning Devices, bells, sirens and remote monitoring
3. Control Panel, to control the various states of the system
4. Power Supplies, including backup batteries

DETECTION DEVICES 

Detection devices do exactly as the name implies, these are the senses of the system and detect intrusion by a number of different means.

One of the most common detection devices is the contact switch which detects the opening of windows, doors, etc. Numerous different types of contacts are available for different applications such as roller shutters requiring large heavy duty types or domestic doors requiring neat flush fitting types.

From a burglars point of view it is some times more convenient to smash their way through a door or window than to open it and some even less desirable methods have been employed for gaining access to a premises. Other types of detection are used where this is a risk. Devices such as lead foil tape can be used for glass sections or closed circuit wiring for semi-solid structures such as doors, walls, etc. These last two types are relatively old forms of detection and although they facilitate a very inexpensive installation they have the disadvantage in that they must be replaced after an attack has occurred.

A more modern device for detecting forced entry is the vibration sensor (or inertia sensor). Primarily it has the advantage, in that it can be easily installed and, coupled with the relevant analyser it can differentiate between different types of vibrations. This makes it very suitable for different structures e.g.; solid walls, glass, wood, etc.

In some cases it is not always cost effective to cover every entry point so units such as motion detectors can be used and in fact these detectors are used quite extensively in modern domestic and commercial systems. A motion detector, as the name implies, detects the motion of an intruder within a certain area. The maximum range of these detectors is about 35 meters.

As you can see there are a wide variety of detection devices for alarm systems and we will go into each one in detail in later sections of the course.