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This FAQ is intended to help individuals new to the concepts involved in a security system in your search for a local alarm installation company.
Please Note: Purchasing an alarm system is very much a personal choice. Whether you decide to obtain the equpiment locally or on line and install it yourself, or have a company install it for you, this FAQ should provide you with some information that will help in making an informed decision with respect to your personal security purchase.
First and foremost an alarm system will not
decrease your chances of having a break-in or burglary. Alarm systems are
designed to detect and inform, not
prevent. At best, what a well designed alarm system will do is detect
the presence of an intruder before he enters the premise and limit the amount
of time he has to grab your stuff.
If this is indeed your first time purchasing a security system, it's a good idea to familiarize yourself with the terminology used in the security industry. Getting a basic understanding of what makes up a modern alarm system, installation methods, and terms used will help you to make an informed decision with respect to your protection.
There are two types of systems (or alarm categories). All modern home and business alarms will fall into one of these two categories. Some are a compromise between the two based on the individual business or home owners budget.
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Perimeter |
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Interior |
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Devices used include:
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Devices used include: |
Note: Perimeter protection is designed primarily to protect the occupants of a building or area and is defined by a specific boundary (usually exterior or interior walls).
Of the two main groups of devices that comprise a modern alarm system, contact type switches are the simplest by far, and the most powerful. When properly utilized, they can detect an intrusion into the protected space even before physical entry is gained. Contacts on certain entry doors also act as "triggers" that enable the system to detect an entry of a legitimate user and give them the time required to access the control unit and disarm (or turn it off).
The most common types of contacts employ a micro switch made of very thin metal reeds that are hermetically sealed into a plastic or aluminum housing. They are either surface mounted or flush mounted into the door or window frame. Surface mounted contacts are usually secured with double sided tape or screwed onto the door frame. Wires connected to the switch terminals are in turn terminated into one of the zones of the control unit. A simple magnet is mounted immediately adjacent to the switch on the door or window itself. When the two units (magnet and switch) are in close proximity, the control unit recognizes this as a "normal" condition. When you open the door/window, the reed switch is activated and the alarm system interprets this as a "break" in the wire which in turn triggers the zone to which the switch is terminated.
Most alarm systems are capable of recognizing when a switch is "tampered" with, and it is up to you as the concerned customer (not the alarm installer) to ensure that this feature is activated. In most instances, most alarm companies will install "low security" normally closed switches and in the case of a flush mounted installation, this provides excellent protection. Surface mounted switches, however, are far more accessible to a knowledgeable burglar or thief, and in some applications a higher security switch may be the more prudent choice. Your professional security consultant should present these options to you during the course of his normal walk around inspection of your premise. In most instances the difference in cost between the lower and the higher security switches is not even worth mentioning.
Some alarm systems require even higher security contacts. These employ a reed switch with three terminals. When an "alarm" condition is achieved (by the opening of a door or window), one "side" of the terminals will "open", and the other will "short". The combination or a single action (an opening or closing terminal) will result in a faulted or tripped zone. Still other types of contacts employ a "biassed" magnet/switch combination. When an intruder attempts to bypass the magnet on the door or window with another magnet, the switch will immediately open and display an alarm condition. The simplest contact switch device is one that is rarely utilized today, althought there are still legitimate applications that do crop up from time to time. This device employs a spring loaded microswitch, which looks very similar to the switches used in your car to turn on the interior lights when you open your door.
One of the most innovative devices and probably the best physical intrusion sensor on the market today. This device responds to specific audio frequencies associated with breaking glass. It consists of a sensitive microphone mounted inside a plastic case and quite often is "teamed" with either a seismic or air density sensor. The two technologies working in tandem provide a virtually false alarm free detector. The physical act of dropping a glass on a tile floor directly beneath one of these types of sensors was usually sufficient to trigger a false alarm. The industry has addressed this problem by providing "dual-technology" sensors.
When an exterior window pane is broken the glass itself actually "flexes" or bulges in the few microseconds after an impact and just before it physically breaks or shatters. This action, coupled with the sound made by the breaking glass is how the sensor is able to distinguish between an actual window being broken, and the accidental dropping of a drinking glass. "Flex" is by no means the only other part of the "dual-technology" equation. Other sensors incorporate what resembles a seismic sensor as part of their alarm discrimination circuitry. These types of sensors have to be mounted fairly close to the windows they are protecting, and their installtion requires other "additional" considerations. They have to be attached to a portion of the building structure that is capable of transmitting the "shock" part of the equation. This may not always be possible.
Your alarm consultant will also caution you with respect to curtains, and other window "treatments" that may interfere with the sensor and preclude it from actually detecting an intrusion. It's also very important for the installer to verify the sensor's capacity to detect an alarm condition prior to it's actual physical installation. What this means is that the installer should manually test each detector BEFORE determining the unit's final installation location.
Here are some pictures of different dual technology glass break detectors:
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Another type of glass breakage sensor actually sticks to the window glass. It's either in the form of a silver (or gold) foil that runs around the perimeter of the glass pane, or in the shape of a one inch square or round plastic button with wires coming from it. The foil has to be physically broken (which usually happens when the window it's stuck on is smashed). The "bug" I mention is more of a shock sensor. A sharp rap on the pane with a screwdriver or other hard object will usually cause it to "alarm".
This simple technology utilizes your existing window and door screens (in most instances). Your installer will remove your screens and have them replaced with ones that have a very thin (36AWG) stranded wire woven in. When in place, any attempt to cut or tamper with the screen will result in an alarm condition. Window screens allow you the luxury of opening the protected window and enjoying the fresh air secure in the knowledge that if someone tries to gain access through the window, the alarm will sound.
are not to be confused with motion detectors. Most often they utilize infra-red light energy, but instead of being "passive" (that is strictly an infra-red sensor), a beam system requires two separate elements to complete the "circuit", namely an emitter and a receiver. Both these units are mounted facing each other. The emitter shines a beam of infra-red light at the receiver. When the beam is broken, the receiver trips the alarm. A less expensive "cousin" to this type of unit is usually seen in a lot of retail stores. When a customer enters the store, he usually "breaks the beam" and a chime or buzzer is sounded to alert the shopkeeper to the presence of the patron. In a security system, beam detectors can literally become invisible "walls" or "curtains" of protection, and since the detectors housings can be easily disguised or hidden, an intruder usually won't know where or when he breaks the beam.
Note: Interior protection is designed primarily to protect objects and personal property. Most often these devices are bypassed when the room or area is occupied by the legitimate owners or users.
Unauthorized access or intrusions into a protected area are best detected by movement (or motion) sensors. These types of units utilize a variety of methods to sense motion of an individual. These methods are:
Infrared (PIRO ELEMENT) Detectors
Commonly referred to as PIR's (short for Passive InfraRed) detector. The most common type of detector utilized today, and the most cost-effective. All are referred to as "dual element" detectors which, simply put, allows them to discriminate between commonly encountered background "noise" and the physical presence of an intruder. These detectors sense infrared energy emitted by or reflected from an object. Infrared energy is simply heat. All objects in a room emit some form of heat energy, some more than others. Humans and household pets (dogs & cats) emit a lot of infrared energy in the form of body heat. We are surrounded by a "halo" of infrared energy. We can't see it ourselves, but these detectors are designed specifically to sense it.
Some areas of a room can also emit a lot of infrared light or heat. A fireplace or a patch of floor illuminated by the sun for long periods of time produce a "bloom" of infrared light that is brighter than any living target.
The way PIR's work is actually quite ingenious. The actual detection element is mounted behind a faceted lens usually made of an opaque plastic. This plastic is essentially a light filter. It allows free passage of infrared light, but restricts other bands of light (the middle oranges, yellows, greens, and blues (or ultraviolet) commonly referred to as a "white light" filter.
A moving target or object passes in front of the lens. As it moves from one facet to another circuitry in the detector "times" the movement from facet to facet. When it falls into a preprogrammed set of variables (most often associated with a moving target), the "alarm thresh hold" is reached and the sensor is triggered. Unfortunately it is often difficult for the sensor to distinguish between an "animal" target and a human one (such as an intruder). Larger animals will often trigger "false alarms". Your security consultant should ask about pets and may even suggest restricting their movements (closing off the areas protected by motion sensors to the pet) to avoid the possibility of false alarms. New technology has advanced the capability of the PIR sensor, and "pet friendly" detectors are now widely available. Pet immune or pet friendly detectors are more expensive than standard motion sensors, but this is an option you may well wish to consider. These are pictures of some of the more popular infrared sensors used today:
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Ultra-sonic Detectors
These are motion sensors that are rarely utilized today because of the advances made in the PIR detector and the shortcomings identified with this technology. These types of detectors utilize high frequency sound (a frequency well beyond human hearing) and something called the "Doppler Shift" (an effect caused by a target or individual moving towards the sensor) which activates detection circuitry and causes the sensor to "alarm".
Unfortunately over time, the high frequency sound emitted by the sensor can become modulated to a lower frequency and begin to disturb pets in the home. Cats & dogs that refuse to enter certain rooms in the house or act differently when in the same room as one of these detectors are sure signs that the sensor may require adjustment or replacement (usually the latter). The major drawback with these types of sensors is the ease with which they are "cheated". An intruder that recognizes the distinctive shape of the sensor has only to walk through the room PARALLEL to the sensor. As long as he/she doesn't approach the sensor, the "Doppler Shift" essential to the units activation will not occur.
Microwave Detectors
These units are very similar to the ultra-sonic detector with one major exception. Instead of sound energy, this type of sensor utilizes radar energy to sense the "Doppler Shift" caused by a moving target. Because it utilizes radar (microwave) energy it can also sense "side" Doppler (that is movement parallel to the sensors line of sight), so the drawback encountered with the ultra-sonic detector is virtually eliminated. Unfortunately and because it utilizes this technology, it can also pass hrough some types walls or barriers. It can also sense the movement of liquids in household water and drain pipes. It's ability to be focussed very tightly and it's uncommon range (some units can "see" three hundred feet or one hundred & eighty metres or more) makes it an excellent fence line protector.
FLOOR MATS AND STRESS SENSORS:
These devices are specially designed to be concealed either under room carpet (or rugs) or under the floor. When an intruder steps onto the protected floor, he triggers the alarm. These sensors are more commonly used in highly travelled areas (like hallways), or surrounding a specific area or object that requires protection.
For more information on specific security concerns you might have, please email me, or feel free to contact one of the on line Dealers represented here:
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Last updated:
October 27, 2003
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