#alarm
Alarm is a collective term for devices that alert about burglary, attack, sabotage, fire and similar emergency situations.
Their task is to electronically monitor the objects being monitored and promptly notify about an emergency situation.
Depending on the design of such a system, various tasks can be envisaged for it. However, alarm systems cannot actively counteract threatening factors.
Only in combination with reliable mechanical means and appropriate organizational measures (i.e. actions upon alarm signal) is an optimal level of safety achieved.
With the help of alarm systems, the alarm signal is reliably and immediately transmitted to the rescue services, which allows for the maximum possible reduction of possible damage.
The methods of warning about danger must be proportionate to the existing risk. It does not matter whether it is given on site (siren, flashing beacon) or transmitted externally (via cable), the main thing is that the police or fire department arrives at the scene of the incident in time.
Not every burglar panics and runs away when the alarm goes off: many of them accurately calculate the time remaining until the police arrive, or rely on the complete indifference of neighbors.
The advantage of an alarm system is that it can detect a break-in or attempted break-in as early as possible and alert the security service.
Alarm systems are used to monitor a protected property during the absence, and in some cases during the presence, of residents.
Components of the device
Each alarm system mainly consists of four components:
• a system unit;
• sensors;
• controls;
• an alarm device.
The following pages will cover this in more detail, but first we will look at the requirements that a reliable alarm system must meet:
• To avoid false alarms, alarm systems should be as independent as possible from weather conditions and other interference.
• The system should be tailored to the specific facility, taking into account its vulnerabilities.
• The system should be easy to operate for the user.
• Installation and maintenance work must be carried out by professionals. Furthermore, the Association for Damage Prevention (VdS) stipulates that the installation, commissioning and maintenance of alarm systems must be carried out by a licensed specialist company.
• The alarm system must be of high quality. Currently, the Loss Prevention Association recognizes both cable and radio systems. However, in any case, their acceptance and assessment must be carried out by a specialist of the Association.
Certification of the Loss Prevention Association. For citizens living in private residential premises with valuables worth up to 100,000 euros, property insurance companies recommend installing Class A systems.
In this case, individual vulnerable areas are monitored by motion sensors and at least a local alarm signal (flashing beacon and siren) must be given. For a cost of over 100,000 euros, a class B burglar alarm system is required. In addition to internal surveillance, all possible entry points (windows, doors, pits) must also be monitored. The alarm signal must be transmitted to a licensed security company via a dialer at the same time as the local signal is given.
Alternatives.
For homeowners who are primarily concerned with the presence of a burglar alarm rather than the insurance premium, there are some alternatives:
• wireless systems;
• small-sized devices;
• door locks with alarm.
I would like to draw your attention to alarm systems with radio signal transmission. They are easy to install. However, the ease of installation is associated with a higher cost of the device compared to cable systems.
System unit
The heart of any security alarm system is the system unit. Here are its main functions,
• Receiving all signals from sensors (burglar sensors, alarm button).
• Monitoring and control functions (self-checking of operability and power supply).
• Evaluation of signals from controls (blocking lock, control panel).
• Sending an alarm signal (siren, flashing beacon, autodialer module, direct line to the police).
The alarm system units are modular and have a variety of programming options, allowing the device's operating mode to be set depending on the specific features of a particular protected facility. Small units can have up to four communication lines with sensors; this is usually enough to ensure the security of a single-family home.
With higher security requirements and larger protected facilities, four to ten communication lines with sensors may be necessary. Using additional devices, the number of sensor groups can be increased indefinitely.
The system unit monitors the resistance value in each group of sensors. More complex units are equipped with locking buttons that allow individual groups to be switched off. Thanks to this, such a system can be used both when residents are absent and when they are present in the house.
To avoid spontaneous false alarms, a delay in triggering the alarm and sending an alarm signal must be provided.
The system unit must be located in a protected place inside the guarded premises to avoid its deliberate failure. For reliable power supply, in addition to the mains power supply, an additional power source capable of operating autonomously for at least 60 hours must be installed.
Since such devices are not cheap, and handling them requires skills, it is necessary to pay special attention to their installation and be sure to consult with a specialist.
Planning the placement of the system
Before installing a security alarm system, a number of issues related to the security of the home must be carefully analyzed.
It is necessary to identify all vulnerabilities and decide:
• Does the insurance company require the installation of an alarm system to reduce its risks?
• Are there valuables in the house that require special protection through additional security measures?
• Is the safety of the residents at increased risk, which requires the installation of an attack notification system?
• How long will it take for the police or security company to arrive at the scene of an incident after an alarm has been triggered?
The effectiveness of your entire planned security system depends on the quality of the system unit.
There are two main types of such systems: protection during absence and protection during the presence of residents.
Protection during absence
It implies full protection of the entire home, starting with internal surveillance in the premises (usually by means of motion sensors: infrared, ultrasonic or radar). During absence, the user turns on the alarm from the outside, i.e. while outside the building. In the event of a break-in or an attempt to disable the system, the security alarm immediately gives a general alarm signal.
A reasonable addition to such a system is continuous protection of the entire perimeter of the object, consisting of sensors for opening windows, doors, etc. You can also install trap sensors at the entrance and in the corridors. Particularly valuable objects should be protected separately.
Protection during presence
The task of this system is to guarantee you a peaceful sleep. At the same time, the alarm controls individual parts of the house. Residents do not need to fear an unexpected attack or robbery while they are sleeping or busy with something.
Perimeter security devices can be used for protection during presence. In this case, internal surveillance devices cannot be used so as not to restrict the freedom of movement of residents in their own home. The alarm is turned on and off during presence inside the premises on the system unit or using separate controls. At the user's discretion, different alarm signals can be set: an internal preliminary signal or a general signal with a delay. Properly located hand alarms and emergency call buttons are designed to ensure your personal safety.
Protection against attempts to disable the system
The device monitors the resistance value in all its lines. The system unit perceives any changes (for example, breaks) as an attempt at unauthorized interference. In addition, all device covers are protected from removal, so that when the alarm is on, any attempt to do anything with the sensors, alarms and the unit itself leads to an immediate external alarm signal. Manual alarms are usually equipped with the same protection system against attempts to disable them. All high-quality devices must be protected from external manipulation.
Modern technologies
The new generation of security alarm systems is based on the most modern technologies, providing for the transfer of data between all elements of the device.
The next step into the future involves the use of modern means of data transmission: when controlled remotely, they provide immediate transmission of all information about the state of the system.
Security alarm sensors
Sensors are, so to speak, the guard posts of the security alarm system. They are placed on the walls, doors and windows of the premises and serve to detect an attempt to intrude on the observed object.
Depending on their purpose, the following types of sensors are distinguished:
• internal surveillance sensors;
• perimeter security sensors;
• manual alarms.
It is advisable to divide the protected area into several segments, each of which is responsible for a separate group of sensors. The number of sensors in one group should not exceed twenty.
Typically, security alarm systems have several cables for communication with perimeter security sensors, internal surveillance in the premises of various zones and floors of the protected facility, cables of manual alarms, as well as cables of the system of protection against attempts to disable and functional control of the device.
The operation of communication cables of alarm systems, or circuits, is based on the use of the principle of quiescent current.
Circuits using working current, due to their vulnerability to attempts to disable, are suitable only for manual alarms.
As a rule, all sensors of one group are connected in series into one circuit. A quiescent current flows from the system unit through the sensors. In this case, the entire circuit, if it is not divided into sections, has a certain total resistance.
Only in the most modern devices is it envisaged that each sensor has its own resistance value.
When current flows, the total resistance of the entire circuit leads to a known decrease in voltage, the value of which is measured in the system unit.
In the event of a sudden change in voltage (when a sensor is triggered or an attempt is made to manipulate it), the system unit gives an alarm signal.
The sensors and controls are connected by a flexible cable with a cross-section of at least 0.14 mm.
For sensors in a circuit that is not divided into sections, cables with four cores of the same polarity should be used to protect against attempts to disable them.
Cables should always be selected in accordance with their specifications and laid in protected areas as inconspicuously as possible. Appropriate connecting devices must be provided to connect the cables.
Internal surveillance
The term «interior surveillance» means that certain parts of the home are monitored to prevent unauthorized persons from entering.
Most motion sensors use infrared radiation. They react to the heat emitted by the human body.
If a person appears in the monitored area, a temperature difference occurs, which is registered by the electronics and an alarm is sounded.
For indoor surveillance, motion sensors that respond to the movement of an object in three-dimensional space are mainly used.
Ultrasonic motion sensors and radars (high-frequency sensors) are used very rarely. If a person moves within their range, a reflected signal of a changed frequency is returned to the sensors. This frequency shift, registered by the sensor, is called the Doppler effect.
Relay barriers can work with visible light, infrared radiation or ultrasound. They are triggered by interrupting the beam sent from the emitter to the receiver.
Vibration sensors are used to monitor containers with valuables and safes. They
Professional advice
Sensors and sensor devices located around the perimeter of the premises should recognize an attempted break-in in advance and be triggered before the intruder can enter the protected area.
react to shaking and vibration of objects to which physical force is applied.
Perimeter protection
Perimeter protection is understood as the protection of all vulnerable external areas of the protected object, so the first task is to identify such vulnerable areas.
These usually include doors, glass surfaces, hatches, as well as roofing and weak areas of masonry.
A necessary prerequisite for effective perimeter protection is the presence of reliable locks on all external openings of the house.
Magnetic sensor devices— these are sensors that are installed on each window sash, door frame and skylight and ensure that they are in the closed position.
When the alarm system is set in the house, these sensors confirm that all windows and doors are closed. In the event of a break-in attempt, when the circuit is interrupted, the sensors transmit an alarm signal to the system unit.
Mechanical sensor devices.
Unlike magnetic sensors, mechanical sensors react much more to moisture and dirt and are therefore used less and less often.
Glass break sensors.
Glass break sensors are glued directly to window panes and give an alarm when they are mechanically damaged.
Glass break sensors contain small quartz plates that sense vibrations of a specific frequency generated by cracking glass.
Hand-held alarms for your personal protection should be placed in suitable locations, such as at entrance doors and in bedrooms. Portable alarms can also be used.
Hand-held alarms.
Hand-held alarms (emergency call buttons) are used to sound an alarm in the event of danger.
Turning the alarm on and off
Even if you leave your home for a short time, you should always turn on the security alarm.
An external device for switching on/off the alarm is usually installed on any door through which one can leave the house (a door with a blocking lock).
According to the «principle of compulsion», other doors cannot be locked after the alarm is switched on. When the alarm is switched on, any activation of the sensor or the protection system against an attempt to disable it will result in an alarm signal.
To monitor the operation of the system, the controls can be equipped with devices for confirming the system's activation and indicator lamps.
External control devices
To switch the alarm on/off from the outside, a blocking lock is usually used, installed on the last exit/first entrance door of the protected facility. It should allow control only from outside the premises and be equipped with a control indicator showing the current alarm status.
Blocking locks with a profile cylinder can be integrated into any lock system. They must be protected from any attempts to break in.
Currently, there are also electronic cylinder mechanisms that perform the function of a blocking lock.
External contactless control elements are also currently recognized as equivalent control elements.
A switch-lock can also be included in the alarm system, which simultaneously locks the door and turns on the alarm (when the lock is opened, the alarm is automatically turned off).
Internal control devices
Using the system unit or separate control systems, you can turn on the security alarm system without leaving your home. You can also monitor its status.
Alert devices
The figure below shows various alert devices: a flashing beacon, a siren, an internal alert device, various automatic and digital data transmission systems. The latter immediately transmit an alarm signal to the security company via a telephone cable or a direct line.
Audible and visual alarms.
An alarm is usually signaled by a siren and a flashing light or flashing lamp, sometimes connected to all the outside lights of the house.
The primary purpose of this «loud» alarm is to put the burglar to flight as soon as possible, once he realizes that he will not have enough time to carry out his plan to the end.
It makes sense to tell your neighbors about the alarm system; They should also know exactly what to do when an alarm sounds.
Insurance companies require that Class A and B alarm systems have two independent sirens and one flashing light.
«Silent» alarm
Another technical option is a «silent» alarm, in which the signal is transmitted via a cable to the nearest security service.
A direct line to the police station can only be installed in the event of a particularly high level of threat, and its use is associated with fairly high costs.
With a «silent» alarm, there is a high probability of catching a burglar red-handed.
Internal alarm
It often seems reasonable to delay the general alarm for a few seconds after the «internal» acoustic signal.
A tenant who calls carelessness triggering the alarm, can correct the error and have time to turn off the alarm.