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1.0 ANTI-THEFT SYSTEMS AND TYPES OF CONNECTION
1.1 THE ANTI-THEFT SYSTEM
In simple terms, an anti-theft system is made of three types of components: detectors, control and computing box
and signalling devices. These components are usually separated, but sometimes one single device can include
more than one of them. Let’s now analyse the tasks of these components and the names under which they are
known. The term detector refers a device which is able to identify changes - voluntarily or not - which can happen
to an element or to a physical characteristic of the environment in which they are situated. Detectors, as their name
refers, are for the anti-theft system the equivalent of our senses. Later, we will explain the main type of detectors in
more detail.
The control and computing box is the “brain” of the anti-theft system and it carries out many tasks:
It interprets the different signals which arrive from the detectors and consequently starts the most suitable
actions, such as for example, ignoring the opening of the INPUT door if the anti-theft system is deactivated or
sending an alarm if the same signal is received when the anti-theft system is on;
It verifies that all the system devices are always working;
It signals possible faults which could threaten the security and functioning of the system;
It records all the main events.
It is exactly for these characteristics that every anti-theft system has only one control panel. Lastly, the signalling
devices are able to inform people or other systems or devices about a situation which could be dangerous for
people or goods placed under the anti-theft system protection. Siren, telephone dialler and communicator, are
some of the names which identify this type of device. The anti-theft system is completed by other accessories
which make its use easier, such as remote controls, commutators and activation key pads. All these devices
enable the anti-theft system to reach its objective: promptly inform if there is a threat to the goods and the people it
must protect.
1.2 TYPE OF DETECTORS
Anti-theft detectors are divided according to:
Their working principle, or the
Type of action they must signal, or the
Place they must be applied to or what they must check, or the
Physical characteristics of the environment they must monitor.
The following are the most common types of detectors which can be part of an anti-theft system.
1.2.1 KEY
This is definitely the detector which is simpler to use. There are many types, from those which must be activated by
hand to those with a rod or those which can be pressed with a foot.
1.2.2 MAGNETIC CONTACT (REED) or OPENING CONTACT
This is the simplest type of detector and it is used to check the opening of doors and windows. The opening contact
is made of two parts: a magnet and a lamellar contact. When these are situated side by side, a few millimetres
apart, the magnetic zone manages to keep the lamellar contact which closes an electrical circuit in its position.
When they are moved apart, the magnetic zone strength diminishes, the lamellar contact loses its position and the
electrical circuit is interrupted, thus producing an alarm signal. The magnet must be applied onto the panel or onto
the window or door leaf and the lamellar contact onto the frame, as far as possible from the hinges, so that it is
sufficient to slightly open the door or window to interrupt the circuit. There are many which satisfy different aesthetic
and technical needs (wooden doors and windows, armoured doors, built-in contacts, etc.). This type of detector is
in charge of “perimeter” protection.
1.2.3 ROPE CONTACT FOR SHUTTERS
This device must be positioned inside the shutter box and it contains an automatic rope winder joined with an
impulse counter. When the end of the thin rope is connected with the lower part of the shutter, every time the
shutter is lowered or lifted the rope winder rotates and produces impulses which are detected by the counter. This
causes an alarm signalling and enables the windows and the shutters to be kept slightly open to change the air
whilst guaranteeing “perimeter” protection.
1.2.4 GLASS BREAKING DETECTOR
This is used to signal the breaking of shop windows, big windows and skylights. It is glued directly onto the glass or
crystal to be protected and it registers the oscillations caused by the glass breaking, causing an alarm signalling. It
is used both for “perimeter” protection and for the protection of showcases and cabinets.
