Burglar (or intrusion), fire and safety alarms are found in electronic forme today.
Sensors are connected to a control unit via either a low-voltage hardwire or narrowband
RF signal, which is used to interact with a response device. The most common security
sensors indicate the opening of a door or window or detect motion via passive infrared
(PIR). New construction systems are predominately hardwired for economy while in
retrofits wireless systems may be more economical and certainly quicker to install.
Some systems are dedicated to one mission, others handle fire, intrusion, and safety
alarms simultaneously. Sophistication ranges from small, self-contained noisemakers,
to complicated, multi-zoned systems with color-coded computer monitor outputs. Many
of these concepts also apply to portable alarms for protecting cars, trucks or other
vehicles and their contents (i.e., "car alarms"). See also fire alarm control panel
for specific fire system issues. Burglar alarms are sometimes referred to as alarm
systems, see burglar alarm control panel for a discussion of hard-wired burglar
alarm system design. Burglar alarms (or perimeter detection systems, Perimeter protection,
intrusion detection systems and many more terms for the same thing) are divided
to two main fields: home burglar alarms and industrial burglar and perimeter intrusion
detection. Home burglar alarms This kind of burglar alarms would be most of the
time low budget alarm systems assembled mainly from cheap (most of the time Chinese
detectors) infrared red detectors that the home owner or the security contractor
will install in front of all the windows and doors in the house.
The infrared sensors in most of the homes today are for indoor use only because
if they would be installed outdoor the amount of the false alarms would be large
and ineffective. Installing outdoor sensors cost is higher and they are also not
false alarm proof The other part of protecting a house to put magnetic sensors on
the doors and windows, those sensors will alarm the system ONLY when door or window
was opened and not for example window broken in. The sensors would be connected
most of the time to a simple control panel with code and basic display. The control
panel will be connected most of the time to siren and a dialer who calls the owner
or the police or both. This is the basic form of home alarm system. Industrial perimeter
intrusion detection systems In the field of industrial security systems, the methodology
of protection is quite different. First is to detect, second to delay and third
to alarm. In that way of thinking industrial alarm systems are designed as an integration
of few sensor systems. The most important for big facilities would be the outer
fence with sensor on it which would detect and delay the intruders before they even
reach the building itself> As described below, there are about five fence mounted
sensors which each one of them has its own pros and cons in aspect of price, durability
and false alarm rate. Other then the fence mounted sensors there are the buried
perimeter sensors that can be put on top of a wall or buried underground to create
a hidden defense line who only detects and not delays. The next alignment of detecting
would be the Closed Circuit Television (i.e CCTV) in the field there would be also
2 kinds. One a guard who watch the camera screens or another solutions and the smart
one would be video motion detection software who analyze the video and can detect
breaches in the perimeter. In any case CCTV is ineffective as a standalone sensor
because it’s affected by weather conditions as cameras cannot see in heavy fog,
rain and snow. The last line of protection is the building itself most of the time
who would be protected by infrared sensors, microwave sensors, smart locks and magnetic
door sensors.
Alarm types Indoor These types of sensors would be found most indoor because of
false alarms and weather durability they are most effective for indoor use. Passive
Infrared Detectors The passive infrared detector (PIR) is one of the most common
detectors found in household and small business environments because it offers affordable
and reliable functionality. The term passive refers to the fact that the detector
is able to function without the need to generate and radiate its own energy (unlike
ultrasonic and microwave volumetric intrusion detectors that are “active” in operation).
PIRs are able to distinguish if an infrared emitting object is present by first
learning the ambient temperature of the monitored space and then detecting a change
in the temperature caused by the presence of an object. Using the principle of differentiation,
which is a check of presence or nonpresence, PIRs verify if an intruder or object
is actually there. Creating individual zones of detection where each zone comprises
one or more layers can achieve differentiation. Between the zones there are areas
of no sensitivity (dead zones) that are used by the sensor for comparison. Ultrasonic
Detectors Using frequencies between 25 kHz and 75 kHz, these active detectors transmit
ultrasonic sound waves that are inaudible to humans. The Doppler shift principle
is the underlying method of operation, in which a change in frequency is detected
due to object motion. This is caused when a moving object changes the frequency
of sound waves around it. Two conditions must occur to successfully detect a Doppler
shift event: * There must be motion of an object either towards or away from the
receiver. * The motion of the object must cause a change in the ultrasonic frequency
to the receiver relative to the transmitting frequency. The ultrasonic detector
operates by the transmitter emitting an ultrasonic signal into the area to be protected.
The sound waves are reflected by solid objects (such as the surrounding floor, walls
and ceiling) and then detected by the receiver. Because ultrasonic waves are transmitted
through air, then hard-surfaced objects tend to reflect most of the ultrasonic energy,
while soft surfaces tend to absorb most energy. When the surfaces are stationary,
the frequency of the waves detected by the receiver will be equal to the transmitted
frequency. However, a change in frequency will occur as a result of the Doppler
principle, when a person or object is moving towards or away from the detector.
Such an event initiates an alarm signal. This technology is considered obsolete
by many alarm professionals, and is not actively installed. Microwave Detectors
This device emits microwaves from a transmitter and detects microwaves at a receiver,
either through reflection or reduction in beam intensity. The transmitter and receiver
are usually combined inside a single housing (monostatic) for indoor applications,
and separate housings (bistatic) for outdoor applications.
By generating energy in the microwave region of the electromagnetic spectrum, detector
operates as an active volumetric device that responds to: * A Doppler shift frequency
change. * A frequency phase shift. * A motion causing reduction in received energy.
Photo-Electric Beams Photoelectric beam systems detect the presence of an intruder
by transmitting visible or infra red light beams across an area, where these beams
maybe obstructed. To improve the detection surface area, the beams are often employed
in stacks of two or more. However, if an intruder is aware of the technology’s presence,
it can be avoided. The technology can be an effective long-range detection system,
if installed in stacks of three or more where the transmitters and receivers are
staggered to create a fence-like barrier. Systems are available for both internal
and external applications. To prevent a clandestine attack using a secondary light
source being used to hold the detector in a ‘sealed’ condition whilst an intruder
passes through, most systems use and detect a modulated light source Glass Break
Detectors The glass break detector maybe used for internal perimeter building protection.
When glass breaks it generates sound in a wide band of frequencies. These can range
from infrasonic, which is below 20 Hertz (Hz) and can not be heard by the human
ear, through the audio band from 20 Hz to 20 kHz which humans can hear, right up
to ultrasonic, which is above 20 kHz and again cannot be heard. Glass break acoustic
detectors are mounted in close proximity to the glass panes and listen for sound
frequencies associated with glass breaking. Seismic glass break detectors are different
in that they are installed on the glass pane. When glass breaks it produces specific
shock frequencies which travel through the glass and often through the window frame
and the surrounding walls and ceiling. Typically, the most intense frequencies generated
are between 3 and 5 kHz, depending on the type of glass and the presence of a plastic
interlayer. Seismic glass break detectors “feel” these shock frequencies and in
turn generate an alarm condition. Outdoor These types of sensors would be found
most of the time mounted on fences or installed on the perimeter of the protected
area. Vibration (Shaker) or Inertia Sensors These simple devices are mounted on
barriers and are used primarily to detect an attack on the structure itself. The
technology relies on an unstable mechanical configuration that forms part of the
electrical circuit. When movement or vibration occurs, the unstable portion of the
circuit moves and breaks the current flow, which produces an alarm. The technology
of the devices varies and can be sensitive to different levels of vibration.
The medium transmitting the vibration must be correctly selected for the specific
sensor as they are best suited to different types of structures and configurations.
More sophisticated sensors use piezo-electric components rather than mechanical
circuits, which can be tuned to be extremely sensitive to vibration. These sensors
are more durable and more resistant to tampering. * pros: Very reliable sensors,
low false alarm rate and middle place in the price range. * cons: Not many for those
kind of systems. Must be fence mounted would be the main con. People always wants
cheaper but most of the other sensors can't really compete with the Vibration sensors.
conclusion:The best money for value fence mounted configuration. Passive Magnetic
Field Detection This buried security system is based on the Magnetic Anomaly Detection
principle of operation. The system uses an electromagnetic field generator powering
with two wires running in parallel. Both wires run along the perimeter and are usually
installed about 5 inches apart on top of a wall or about foot buried in the ground.
The wires are connected to a signal processor which analyze any change in the magnetic
field. This kind of buried security system sensor cable could be buried on the top
of almost any kind of wall to provide a regular wall detection ability or be buried
in the ground. * pros: Very low false alarm rate, can be put on top of any wall,
very high change to detect real burglars. * cons: Can't be installed in near high
voltage line or radars and airports. conclusion: The best solution in the buried
sensors range. E-Field This proximity system can be installed on building perimeters,
fences, and walls, and also has the ability to be installed free standing on dedicated
poles. The system uses an electromagnetic field generator powering one wire, with
another sensing wire running parallel to it. Both wires run along the perimeter
and are usually installed about 800 millimetres apart. The sensing wire is connected
to a signal processor that analyses: * Amplitude change (mass of intruder), * Rate
change (movement of intruder), * Preset disturbance time (time the intruder is in
the pattern). These items define the characteristics of an intruder and when all
three are detected simultaneously, an alarm signal is generated. The barrier can
provide protection from the ground to about 4 metres of altitude. It is usually
configured in zones of about 200 metre lengths depending on the number of sensor
wires installed. * pros: concealed as a buried form. * cons: expensive, short zones
which means more electronic (more money), high rate of false alarms as it might
sound as it can define a cat from a human in reality it doesn't work that well as
well as extreme weather causes false alarms. conclusion: As in the buried security
systems field the Passive Magnetic Field Detection will do a better job most of
the time.
Microphonic Systems Microphonic based systems vary in design but each is generally
based on the detection of an intruder attempting to cut or climb over a chainwire
fence. Usually the microphonic detection systems are installed as sensor cables
attached to rigid chainwire fences, however some specialised versions of these systems
can also be installed as buried systems underground. Depending on the version selected,
it can be sensitive to different levels of noise or vibration. The system is based
on coaxial sensor cable with the controller having the ability to differentiate
between signals from the cable or chainwire being cut, an intruder climbing the
fence, or bad weather conditions. The systems are designed to detect and analyse
incoming electronic signals received from the sensor cable, and then to generate
alarms from signals which exceed preset conditions.
Remote alarm systems are used to connect the control unit to a predetermined monitor
of some sort, and they come in many different configurations. High-end systems connect
to a central station or responder (eg. Police/ Fire/ Medical) via a direct phone
wire (or tamper-resistant fiber optic cable), and the alarm monitoring includes
not only the sensors, but also the communication wire itself. While direct phone
circuits are still available in some areas from phone companies, because of their
high cost they are becoming uncommon.one Network (PSTN) and raise the alarm, either
with a synthesized voice or increasingly via an encoded message string that the
central station decodes. These may connect to the regular phone system on the system
side of the demarcation point, but typically connect on the customer side ahead
of all phones within the monitored premises so that the alarm system can seize the
line by cutting-off any active calls and call the monitoring company if needed.
Encoders can be programmed to indicate which specific sensor was triggered, and
monitors can show the physical location (or "zone") of the sensor on a list or even
a map of the protected premises, which can make the resulting response more effective.
For example, a water-flow alarm, coupled with a flame detector in the same area
is a more reliable indication of an actual fire than just one or the other sensor
indication by itself. Many alarm panels are equipped with a backup dialer capability
for use when the primary PSTN circuit is not functioning. The redundant dialer may
be connected to a second phone line, or a specialized encoded cellular phone, radio,
or internet interface device to bypass the PSTN entirely, to thwart intentional
tampering with the phone line(s). Just the fact that someone tampered with the line
could trigger a supervisory alarm via the radio network, giving early warning of
an imminent problem (e.g., arson). In some cases a remote building may not have
PSTN phone service, and the cost of trenching and running a direct line may be prohibitive.
It is possible to use a wireless cellular or radio device as the primary communication
method. Broadband Alarm monitoring This section is written like an advertisement.
Please help rewrite this section from a neutral point of view.o the owner with details
of which room may be getting flooded. Some alarm systems are tied to video surveillance
systems so that current video of the intrusion area can be instantly displayed on
a remote monitor, not to mention recorded.
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