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Introduction to Intrusion Alarm Systems

Intrusion alarm systems are designed to detect unauthorized entry into a building or outdoor area. The goals of an intrusion alarm system can be to warn occupants of an intrusion, scare aware the intruder, notify the appropriate authorities that a break-in is occurring, or some combination of all of these. The typical intrusion alarm system consists of the following basic components:


Detection Devices


Detection devices are the components used to detect the entry of an intruder into the building. There are dozens of different types of detection devices, each which use a different method of detecting the presence of an intruder. The most commonly used types of detection devices at commercial facilities are:


Contact Switches


Contact switches are installed on doors and windows to detect when the door or window has been opened. Contact switches are most commonly installed on doors and opening windows at the exterior of the building, but may also be installed on interior doors.


There are a wide variety of different types of contact switches available for installation on wood and metal doors, windows, gates, hatches, and other types of openings.


Motion Detectors


Motion detectors are used to detect the presence or movement of people within the building. Motion detectors are most commonly installed in hallways, corridors, and within rooms that contain a high concentration of valuables.


There are several different types of motion detectors available. The most common type of motion detector in use today is the “passive infrared” (PIR) detector. The PIR detector detects the body heat of a person as he passes within the viewing area of the detector.


Glass Breakage Detectors


Glass breakage detectors, as their name implies, are used to detect the breakage of glass. Glass breakage detectors are normally installed near accessible glass windows and doors at the exterior of the building.


Signaling Devices


Signaling devices are the devices that the intrusion alarm system activates when intrusion is detected. Signaling devices serve three purposes:

  • Notify the intruder that he has been detected, hopefully causing the intruder to flee from the premises, or at least causing the intruder to spend less time in the building.

  • Notify neighboring residents and passersby that the intrusion alarm has been activated.

  • Notify any employees that may be in the building that the intrusion alarm has been activated.


There are both audible and visual types of signaling devices. Audible signaling devices include bells, electronic sirens, and voice announcement systems which broadcast alarm messages using a recorded human voice. Visual signaling devices include revolving lights, blinking lights, and electronic strobe lights.


Signaling devices are normally installed on both the interior and exterior of the building.


Arming Stations


Arming stations are the devices used to “arm” (turn-on) and “disarm” (turn-off) the intrusion alarm system.


The two most common types of arming stations are the key switch arming station and the keypad arming station.


The key switch arming station uses a special keyed switch to arm and disarm the intrusion alarm system. In order to use the key switch arming station, the user must have a special key.


The keypad arming station uses a digital numeric keypad, similar to that on a touch-tone telephone, to arm and disarm the intrusion alarm system. In order to use the keypad arming station, the user must know the correct code.


In addition to simply allowing the user to arm and disarm the system, the keypad type of arming station can also provide the user with the ability to perform certain advanced functions which the key switch arming station cannot. These functions include the ability to arm only a certain portion of the system while leaving other parts disarmed; the ability to perform system diagnostic and maintenance functions; and many other advanced functions.


Both the key switch arming station and the keypad arming station normally provide intrusion alarm system “status indicators”. Status indicators are used to give the user visual information concerning the status of the intrusion alarm system.


The key switch arming station normally uses simple indicator lights to display the status of the system. Usually, a green light on the arming station is used to tell the user that all doors have been closed and that the system is ready to arm. A red light on the arming station is normally used to tell the user whether or not the system is armed or disarmed.


The keypad type of arming station can also use indicator lights, but more commonly, the keypad type of arming station provides an “alphanumeric display” instead of indicator lights. The alphanumeric display uses letters and numbers to display system status information using plain English messages.


The alphanumeric display provides a much greater amount of information to the user than simple indicator lights do. In the event that a door in the building has been left open, the alphanumeric display can tell the user exactly which door has been left open. Alphanumeric displays can also indicate system troubles, alarm activity, and many other conditions.


Arming stations are the primary device that the average user uses to interact with the building’s intrusion alarm system. Arming stations are usually installed inside the building near the doors that are used by employees to leave and enter the building. Arming stations may also be installed on the intrusion alarm system control panel.


Control Equipment


Intrusion alarm “control panels” are the heart of the intrusion alarm system. The intrusion alarm control panel is used to process all system operations and activity. All detection devices, signaling devices, and arming stations directly or indirectly connect to the control panel.


Most modern control panels are actually a specialized form of “computer” which include a microprocessor, computer memory, and data communications modems. These control panels are fully programmable to allow the operating characteristics of the intrusion alarm system to be custom-tailored to meet the needs of the building in which it is installed.


Because the average user of the intrusion alarm system usually never needs to interact with the control panel, these panels are normally installed in a secure closet or equipment room.


Alarm Transmission Equipment


Alarm transmission equipment is used by the intrusion alarm system to communicate alarm events and system activity to an off-site location, such as an alarm monitoring central station.


The purpose of the alarm transmission equipment is to notify the police and building security when the intrusion alarm system has been activated. The alarm transmission equipment can also be connected to the building fire alarm system, and can summon the fire department in the event that the fire alarm has been activated. In addition, the alarm transmission equipment can be used to send reports of system troubles and routine system activity, such as “openings” (disarming of the system) and “closings” (arming of the system).


There are several types of alarm transmission systems. The most common type in use today is the “digital communicator”. The digital communicator uses regular telephone lines to communicate alarm messages to the central station. By using regular telephone lines, the digital communicator eliminates the need to lease special data lines between the building and the central station.


Other types of alarm transmission systems include “multiplex”, “derived channel”, “long-range radio”, and “cellular”. These types of systems provide a greater level of security than digital communicators do, but require that special data lines and/or special monitoring services be provided at an extra monthly cost.


Digital communicators are commonly built-in to most modern intrusion alarm control panels, and only need to be programmed to become operational.


Other types of alarm transmission systems, such as long-range radio or cellular, usually require that a separate piece of equipment be installed and connected to the control panel.


Intrusion Alarm Zoning


An intrusion alarm system in a building can include a large number of different contact switches, motion detectors, glass breakage detectors, and other types of detection devices. A large commercial building such as a warehouse may have detection devices numbering in the hundreds.


To better manage a large number of detection devices, most intrusion alarm systems provide some method of grouping detection devices together. The technique of grouping detection devices together is known as “zoning”. Using the zoning concept, multiple detection devices are combined together into single entities known as intrusion alarm “zones”.


Zones are normally created to divide the intrusion alarm system up into various areas that correspond logically with the physical layout of the building.


To better explain this concept, let’s say that a building was constructed with four separate wings: North Wing, South Wing, East Wing, and West Wing.


When designing an intrusion alarm system for this building, it would be natural to create intrusion alarm zones that corresponded with each of these wings. Using this example, four intrusion alarm zones would be created: one for the North Wing, one for the South Wing, one for the East Wing, and one for the West Wing.


All contact switches, motion detectors, and other detection devices installed within each wing would be connected to the zone corresponding to that wing.


Zoning of the system provides the ability to monitor the system on a zone-by-zone basis. When the intrusion alarm system is activated, it will report the zone in which the detection device is located that caused the alarm. For example, when an intruder opens a door in the North Wing of the building, the system will communicate to the alarm monitoring central station that the North Wing zone has been activated. This allows the police and building security to respond to the area where the intrusion has occurred rather than requiring them to search the entire building for the point of entry.


Zoning of the system can provide the ability to arm and disarm the system on a zone-by-zone basis as well. For example, if an employee was coming to the building on Saturday, and only needed access to the West Wing, she could disarm the intrusion alarm system only for the West Wing zone, leaving the intrusion alarm zones for the other three wings armed.


Most intrusion alarms systems allow the user to arm and disarm each zone independently; as well as allowing groups of zones to be armed and disarmed at the same time.


Zoning also provides the ability to locate system troubles on a zone-by-zone basis. For example, if wiring for the intrusion alarm system was cut, the zoning feature would allow the service person to quickly identify the wing where the trouble was located.


In our example, we used only four zones for an entire building. In most actual systems, a larger number of zones would be provided. Most of today’s intrusion alarm systems have at least eight zones; and it is not uncommon for a large intrusion alarm system to have 24, 32, 64 or more zones.


In general, the more zones the intrusion alarm system provides, and the fewer the detection devices per zone, the better the ability to control and monitor the system.


Individual Point Annunciation


Individual point annunciation is similar to zoning, except that every single detection device is connected as an individual, unique “point” that reports to the system independently.


Individual point annunciation takes the benefits of zoning to the extreme, and provides information on not only what area of the building the intrusion has occurred, but indicates specifically what device caused the alarm. The police and building security are ability to respond to the exact door or other point of entry where the intruder has entered. Individual point annunciation can also provide the ability to “track” the intruder as he travels throughout the building.


Individual point annunciation greatly reduces false alarms and service costs because the service person can go directly to the specific device that caused the problem rather than having to check every device connected to a zone.


Intrusion alarm systems which provide individual point annunciation provide the ability to group one or more points into logical entities known as alarm “areas”, each of which can be armed and disarmed separately.


(In a system with individual point annunciation, alarm “areas” are roughly equivalent to the “zones” of a simpler zoned system in terms of the way that they are armed and disarmed.)


Intrusion Alarm Design Concepts


There is a great deal of flexibility in the way an intrusion alarm system can be designed for a building. The designer has a great deal of latitude in selecting the quantity and type of equipment that will be used, and in determining where this equipment will be located.


Depending on the owner’s security requirements and budget, the designer may choose to design a simple, “bare bones” system, or may choose to design a deluxe, “high-security” system. The primary difference between a simple intrusion alarm system and a more elaborate one is the number and type of detection devices used.


For example, in a low-cost “bare-bones” system, the designer might choose to install detection devices only at a few points in the building where he feels that an intruder would be most likely to enter. An example of this type of system would be a building where contact switches were installed only on the entrance doors to the building.


In a “high security” system, the designer considers every possible way in which an intruder could enter the building, and places detection devices in such a manner that the intruder is quickly detected in every case. An example of this type of system is the building where contact switches are installed on every door, glass breakage detectors are placed near every window, and motion detectors are provided in every room.


In the real world, most intrusion alarm systems are designed to fall somewhere in between these two extremes. Most systems provide more protection than the basic “bare-bones” system with contact switches only, but not the comprehensive protection provided by the “high-security” system with detection devices in every room.


Exactly how many detection devices should be provided in any given building, what type of detection devices should be used, and where these detection devices should be placed is the subject of great debate among intrusion alarm system designers.


While each different system designer has his or her own idea of what the best arrangement of detection devices is, there are four basic “design concepts” which are commonly used:


Perimeter Protection Concept


The “perimeter protection” concept provides detection at the exterior or “perimeter” of the building. The goal of perimeter protection is to detect the intruder at the point of entry.


Complete perimeter protection usually requires that contact switches be installed on every perimeter door and opening window, and that glass breakage detectors be installed near every glass door and window on the exterior of the building.


Interior Protection Concept


The “interior protection” concept provides detection within the interior of the building. The goal of interior protection is to detect the intruder once he has gained entry into the inside of the building.


Complete interior protection requires that motion detectors be installed in every room and corridor of the building. Interior protection can also be achieved by installing contact switches on the interior doors of the building.


Combined Protection Concept


The “combined protection” concept fully combines the detection capabilities of both the perimeter detection concept and the interior protection concept.


The combined protection concept utilizes perimeter detection devices, such as contact switches on exterior doors, as well as interior protection devices, such as motion detectors installed in rooms and corridors.


The combined protection concept provides the benefits of both perimeter protection and interior protection, and is commonly used in “high security” applications, such as at a jewelry store or at warehouses that contain high-value merchandise.


Hybrid Protection Concept


The “hybrid protection” concept utilizes some portions of the perimeter protection concept, and some portions of the interior protection concept.


The goal of the hybrid concept is to take advantage of the benefits of both perimeter and interior protection, while at the same time keeping the cost of the system below the cost of the fully “combined” system described above.


The typical hybrid system uses partial perimeter detection and partial interior protection. An example of a system designed using the hybrid concept would be a building where contact switches were installed on perimeter doors, and motion detectors were installed in hallways and corridors. This system does not provide complete perimeter protection (there are no glass breakage detectors), and does not provide complete interior protection (motion detectors are not provided in every room), yet the combination of detection devices together provides a reasonable level of protection for the building.


There is a great deal of flexibility in the way a hybrid system can be designed. The designer may choose to provide full perimeter protection in some portions of the building, and choose to have only partial perimeter protection in other parts of the building. The same is true with interior protection; complete interior protection can be provided in some areas, while partial or no interior protection can be provided in other areas.


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Published May, 2016

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