Technique: The system

The components of an anti-intrusion alarm system

An anti-intrusion alarm system is always composed of three basic parts:

• the alarm center, "brain" of the system, which always provides an activation device (arming / disarming);
• the detectors, which detect intrusion attempts;
• local and / or remote alarm devices (sirens, telephone dialers).
• The detectors send alarm signals to the control panel, which activates 1 expected alarm devices.

Both a simple domestic installation and a complex one of a bank always have these three elements in mind, even if their degree of sophistication and their number can change significantly depending on the application.

The alarm center

It is the unit to which the signals coming from the detectors arrive and from which the alarm devices are activated when there is an intrusion situation.

The control panel performs and monitors the following activities:

• Programming of the system functions.
  The operations for inserting and disarming the system must be simple and clear and easy to understand. The commands to the control panel to activate or deactivate the alarm system are given by devices equipped with a personal security code. These devices can be code keypads, remote controls or electronic keys. Another feature of the control devices is the anti-theft code, useful when the attacker forcibly forces the home owner to deactivate the burglar alarm; by entering a suitable code a silent alarm is sent at a distance through the telephone dialer.
• Reception of alarm and / or tampering signals.
  It is advisable for each detector to correspond to a control panel circuit. This would allow, in case of breakdown or other needs, to exclude the single zone, keeping the rest of the system active: for example, it is possible to exclude the bedroom during the night by keeping the other detectors active.
• Command of alarm devices.
• Power supply.
  The central unit must be equipped with a battery of accumulators that allows adequate autonomy of the system, even in the absence of electricity.

The detectors

These are devices that detect the presence of an intruder, recognizing physical changes in the protected area. Over the years, detectors have been developed that are sensitive to different physical principles, while at the same time improving reliability.

Today, various types of detectors are available on the market that work according to different physical principles:

• magnetic contacts: detect unauthorized opening of doors and windows by disconnecting two normally contact magnetic elements;
• active infrared detectors: composed of beams of infrared light (not visible to the eye), they detect the interruption of the beams caused by the passage of the attacker;
• microwave and ultrasonic detectors: detect the movement of the intruder in an environment;
• Passive infrared detectors: detect the heat emanating from the body of the intruder.

There are also "dual technology" detectors, which integrate two different types of detection technologies (eg microwave + passive infrared or ultrasound + passive infrared). The peculiarity of these detectors is that of being able to integrate the functionalities of the two technologies, allowing to signal the alarm condition only when both have been activated. the advantage deriving from this is that of significantly reducing the incidence of false alarms where the designer deems that the risk exists.

Alarm devices

The alarm signal, that is the communication to someone of the fact that an intrusion attempt is in progress, is the fundamental function of the burglar alarm system and with it the sky closes which begins with the detection. Once the alarm information coming from the detectors arrives at the control unit, the latter memorizes and activates the alarm devices set up to signal this situation.

The alarm signal can be sent remotely and / or locally.

For remote signaling an automatic call device is required that can send alarm messages to remote (telealarm).

The connection to the Police forces, subject to the release of the appropriate authorization by the Police Headquarters is free, while the connection to the operating room of a private Supervisory Institute takes place through contracts that guarantee prompt intervention and offer the possibility to take advantage of further specialized services.

It is also possible to transmit the alarm message to a series of telephone numbers of trusted persons, memorized during installation of the system.

For local signaling different techniques are in use: the best known is that of emitting high intensity sounds, compliant with current regulations, using acoustic devices, such as sirens.

The siren can be equipped with a flasher, which makes it easier to identify the place where the alarm is coming from.

What to communicate in the alarm message

It is essential that the alarm message is accurate and gives all the information necessary for emergency intervention.

A standard message is the following: "Attention, automatic alarm, theft in place at the home of Mr. ... via ... location ... tel. ...

Type of anti-intrusion alarm systems

Wired systems (wired)

The wired alarm system, ie with the system elements connected to each other by conductors (wires), is powered at low voltage and all the components of the system must be connected by a network of cables. Some types of systems have the characteristic of being able to be inserted, with the necessary precautions, in the existing electrical system, without having to break the walls.

Wireless systems (via radio)

Wireless electronic alarm systems, also known as "wireless", use radio waves to transport information and signals (alarms, insufficient battery signals, tampering, ...) necessary for the operation and management of the system.

These signals connect the various devices that make up the system via ether.

Until a few years ago, in Italy our diffusion was rather limited, above all because of the diffidence on the part of installers and users, worried about those who considered the intrinsic problems of this type of equipment: the incidence of false alarms due to radio interference, the radio vulnerability of the system. the life of the batteries that power the sensors and the certainty of the data coming from the sensors.

Today we find ourselves in a completely different situation due to the remarkable technical evolution that allows new applications made possible by increasingly reliable technologies: an example for all that of mobile telephony.

The most significant stages of this evolution in wireless alarm systems are realized with:

• the use of new radio technologies, which gives the system a high degree of security;
• the introduction of new materials for the production of batteries: in this way long operating autonomy is obtained;
• the increasing availability of different types of sensors.

This is why, today, it is possible to realize anti-intrusion systems with wireless systems characterized by performance and reliability comparable to those of wired systems.

The anti-intrusion systems by radio can be totally wireless or partially wireless.

The former are made up of totally "wireless" devices, including the siren and the central unit, while the latter have the alarm central unit connected to the mains and the external wired siren.

Wireless systems operate with radio signals whose frequencies are free of use and authorized by the Ministry of Communications: it is important to note that both the power and the duration of the transmission of the signals do not in any way damage to human health.

A good wireless system must have the following characteristics:

• monitoring the presence of any radio disturbances;
• periodic check of the presence of the system's equipment;
• identification of the status of each individual device (alarm, tampering, low battery);
• unambiguous coding of the equipment that make up the system.

The autonomy of the system, whose equipment is powered by internal batteries, and an important data on which special attention must be paid: normally the autonomies are 2, 3 or more.

Mixed systems

In some cases, security experts recommend using mixed alarm systems. that is, with part of the system built by cable (for example where channels are provided) and part via radio. Usually the cables are laid only to supply the alarm center and the sirens, while the other components work with radio waves.

Embedded systems

They are the combination of active protection measures with passive ones: a form of integral security that is also a valid response to the most sophisticated break-in techniques. For example, in the integrated system, the electronic lock of the security door can be connected to the burglar alarm system.

Comparison of installation solutions

Wire system (wired)

Advantages:

• it is safe because all the components are connected by a network of cables: by cutting the wires, the alarm is triggered immediately;

• the cost of individual devices and usually lower than the corresponding wireless ones.

Disadvantages:

• wiring installation costs are quite high.

Wireless system (via radio)

Advantages:

• the installation does not require masonry work and is carried out in a short time. There is therefore a saving on labor costs; you can easily modify and expand over time and, in case of moving, reinstall in the new house.

Disadvantages:

• the connection between the various components may present, in some particular cases, problems related to radio interference: let's not forget, in fact, that ether is used for many other transmissions. The cost of individual devices is usually higher than those with wires.