An effective electronic alarm – how do you achieve it? – Part I

An alarm system is like a chain; its effectiveness depends on the capability of its weakest link. Therefore, in order to be truly effective, all the components must be up to the job and the design and installation must also be done in a workmanlike manner. We will see step by step which features to look for in the main components which typically form an electronic alarm system for the home: siren, sensors and dialer.

In this first blog we will discover which features a siren must have in order to best perform its role of raising the alarm.


A good alarm system should be equipped with at least two sirens; a lower quality one, but which is sufficiently on view, and a better quality one, which is well hidden. In this way, a possible burglar will to try to put the first one out of action and then, thinking it is safe to go ahead, will trigger the second one.

Photo: Flickr/TimWeber

Photo: Flickr/TimWeber

A good siren must certainly be powerful, but also – and most importantly – it must not be possible to tamper with it by using simple systems, such as covering it with foam or immersing it in a bucket of water [little tricks that are without doubt still used by burglars].

Siren neutralised with polyurethane foam.

Siren neutralised with polyurethane foam.

It must also withstand any blows which attempt to destroy it. The best ones, from this point of view, are those made with a double die-cast metal case.

Example of siren made of die-cast aluminium.

Example of siren made of die-cast aluminium.

The various sirens with which the system is fitted must be powered by separate outputs; if not, all the sirens would be neutralised by just putting out of action the output present, and in fact it would be like having just a single siren.

An article in the MessaggeroVeneto newspaper stated:

“The less technologically minded criminals use foam to eliminate the sound of sirens, they know how to “blind” the ultrasonic sensors and they have the Bulgarian pick for picking the lock of old-fashioned armoured doors (those with double-bit keys) in just a few seconds. The ones who are in more of a hurry simply smash the alarm system control unit with a hammer, drill through a window (and then open the handle with a lever) or remove the cylinder of a door. Even the grilles on windows, if they are lightweight and anchored just on the outside, have proven to be vulnerable.”

Very often, individuals attempting to break in to our homes have not planned in advance (as can be seen in this video, in which the burglar trying to enter the house is surprised in the courtyard by the presence of an anti-intrusion sensor, connected to a siren) but the trick of using foam to put the siren out of action is far too widespread to be ignored. It would therefore be naive to allow this to be used, by installing a single siren of poor quality which is clearly visible, when just a few tips are sufficient to reduce the risk significantly.

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