NAICS: 33-4100 Computer and Peripheral Equipment Manufacturing, 33-4200 Communications Equipment Manufacturing, 33-4300 Audio and Video Equipment Manufacturing, 33-4400 Semiconductor and Other Electronic Component Manufacturing
SIC: 3570 Computer and Office Equipment, 3660 Communications Equipment, 3670 Electronic Components and Accessories, 3860 Photographic Equipment and Supplies
NAICS-Based Product Codes: 33-42901, 33-42902, 33-42903, and 33-4290W
The function of security equipment is to prevent the entry of unauthorized persons into protected spaces, to keep out undesired objects and substances, and to sound warnings when dangers threaten a person, family, or larger group. The purposes served are simple; in the modern situation the methods used to achieve them have become complex. Once we pass beyond structures—fences, walls, doors, barred windows, and locks—we need electric power to work the devices and to signal when they are activated. Over time, simple alarms have evolved into hi-tech machines embedded in complex systems.
Traditional approaches relied on barriers—moats, walls, and narrow or grated windows. Guard dogs and night watchmen held lookout and sounded warnings. Dogs barked, humans shouted. Long before civil defense sirens warned the public of air attacks, tornadoes, fires, or rising waters, people rang church bells to the same effect. Guardians once searched wagons, baggage, and people to discover hidden weapons coming in or stolen valuables going out of spaces. Since then we've renamed our guardians. They've become security personnel. Nevertheless they continue on the job and augment technological means of search at borders, airports, and at the gates of factories. What has changed in modern times is the substitution of devices for people, resulting in the creation of the security equipment industry. Machines are now our first layer of defense. We use basic detection devices and couple them to equipment that makes a not-so-joyful noise while silently sending out communications by wired or wireless channels to those who are supposed to act.
Observers divide the field in various ways, usually by technology used (closed circuit television), the context of an activity (airport security), or the object being protected (the automobile). For overview it is best to use a functional classification of the field into six categories. These are: public warning systems, identity/access control, intrusion control, active surveillance, substance and article detection, and network protection.
Public Warning Systems
Civil defense installation based on sirens, fire alarms triggered by smoke or heat, vehicular alarms that warn motorists of approaching ambulances, fire trucks, and police vehicles belong under this heading as do ordinary battery-powered smoke alarms.
Identity/Access Control (ID/Access Control)
Technologies used to control who comes in or who goes out belong under this category. The protected space may be vast—the entire country—or just a building or a single room. Techniques of identification and methods of checking identities at borders include lash-ups of passport control and databases accessed by computer to identify undesirables. Fingerprinting and computerized fingerprint identification are part of Identity Control. Common technologies involve the use of electronically coded smart and other card readers that open locked doors. Instead of cards, devices may require a would-be entrant to punch in a secret access code. At one end this technology keeps undesirables out; at the other it provides access to the authorized to assets exemplified by machines used by banks to dispense cash to their customers upon insertion of a card and the keying of a password code.
This broad category embraces all types of technical arrangements intended to foil break-ins, vandalism, and burglaries in facilities with no or minimal human supervision. In residential protection the burglar alarm is activated only when the owner is absent. Burglar-protection techniques usually employ motion detection instruments. In office buildings and other large facilities guards may be present, but supervise the building from control rooms surveying a building through video cameras.
Magnets are used in the simplest applications. An intruder may force a lock, but in opening the door he or she will move a magnet from its seat, break a circuit, and set off an alarm. Special devices mounted on window glass can detect when glass is broken by capturing the shock the break produces. Acoustic devices listen to the silence of a residence or other property left empty. They are fashioned to respond to certain levels and durations of noise. An alternative technology makes use of infrared light invisible to the intruder but triggered by his or her presence. Beams of such light crisscross spaces near entrances and set off alarms or send signals to service bureaus when beams are broken. Microwaves at lower frequency do the same job. A device sends out a beam and catches its reflection measuring the time it takes precisely. It sounds an alarm when bodies block the returning echo. Such installations are usually connected both to alarms that make a sizeable racket when set off and also to communications systems that send a message to service agencies staffed at all times. Automobile protection devices respond to motion sensors that go off when car doors, trunks, or windows are opened while the device is activated.
Video systems use television cameras placed unobtrusively but strategically to watch over selected areas indoors or out. The cameras may be disguised as lamps. Signals from the cameras are routed to display monitors. People monitor the monitors. Multiplexing technology is used so that one video screen can display images from multiple cameras in sequence or on demand. In using digital video methods, in-line computers assist the process by comparing a stored to a new image every fraction of a second and detecting change between them, signaling when motion is detected. Such systems can be and usually are equipped to make a record on tape with the images time-and-date-stamped. Digital systems use DVRs (digital video recorders).
Some users want to survey a scene at all times in real time, but inconspicuously. Active surveillance is common in retail stores for foiling shoplifters. Casino managements use video surveillance for supervising casino employees and to detect foul play by clever gamblers. Increasingly school administrators and managers of sports stadia and other public venues employ active surveillance. The technique is also useful for monitoring traffic. In short, such surveillance is suitable for all situations where modestly sized staffs need to overlook extensive spaces.
Substance and Article Detection
Explosives Detection Systems or EDS machines came into use in 1973 when the Federal Aviation Administration (FAA) ordered carry-on baggage to be checked after explosives had been discovered on three airplanes the year before. The 1960s and early 1970s had seen a rash of hijackings as well. Following the September 11, 2001 terrorist attacks, Congress charged the newly formed Transportation Security Administration (TSA) to institute 100 percent baggage inspection. Checked as well as carry-on baggage would henceforth be irradiated. Mechanical baggage inspection is useful for discovering weapons, but its primary purpose is to detect the presence of explosives. The devices rely on techniques based on X-ray imaging combined with computed tomography (CT), the same art used in CAT scans. Tomography is capable of imaging its target slice by slice. Software techniques enable the EDS machines to recognize the physical structure of explosives—more or less. Such machines produce high rates of false positives, but serve to identify items of baggage worth a closer look by a trained dog able to sniff out the chemicals or a person able to recognize a suspicious package.
Explosive Trace Detection (ETD) machines employ a different technique. They suck air from baggage and examine the resulting gas using gas chromatography. By heating the gases and cycling them through the machine multiple times, ETDs are able to identify trace elements of explosives and also of narcotics. The technology was initially developed for forensic purposes and adapted for luggage inspection.
Passengers at airports must pass through gates sensitive to metal. The gates signal the presence of metal carried in or attached to clothing or hidden on the passenger's body. Those who trigger warning signals are further inspected by people wielding hand-held devices able to precisely locate the metal. Such inspection gates and wands are a technology called article detection. The devices are used beyond airports as well to control the entry of the violently-minded into public spaces, such as soccer stadia.
The vast expansion of the Internet in the 1990s, continuing unabated if at a slower rate in the first decade of the twenty-first century, put a vast domain of property at risk—data stored on computers. The World Wide Web had made ever more nodes accessible to hackers bent on theft, vandalism, or mischief. Protecting such properties has become the responsibility of computer staffs in large and small institutions. The job is performed by software techniques. The products are called firewalls, but the industry refers to them as appliances.
Features of Security Equipment
Most security equipment is actually componentry that, by itself, is next to useless. Security is provided by assembling components into systems. These systems, in turn, must be supervised by people. Security installations may be viewed as having three major parts: (1) the actual detector mechanism itself, (2) a wired or wireless communications link, and (3) a supervisory station with controllers, displays, and recorders. Sanyo, for instance, a supplier of video surveillance systems, offers components including cameras, monitors, digital video recorders, analog recorders, multiplexers (for interconnecting cameras and monitors), controllers (for managing the cameras), power supplies, software, and accessories (lenses, mounting brackets, and housings). Within each of these categories Sanyo offers multiple models.
The heart of baggage checking activity is the EDS machine which incorporates the detection technology. To be effective, however, the machine must be part of a larger setup. A conveyor system delivers baggage to the machine. The machine must communicate with its operator by communications lines. The message, in the form of images, appears on a monitor usually at some distance form the EDS machine. The operator has means—a keyboard or pointing devices—to talk to the machine as well. He or she can cause the machine or, rather, its built-in computer, to rotate or otherwise manipulate suspicious images that it has captured and flagged by analysis. Arrangements must be present, as well, to enable the operator to divert baggage from the general flow for further checking. EDS machines are sometimes mobile, thus truck-mounted, so that they can be moved to the vicinity of airplanes. Baggage transferred directly from one plane to another can then pass through a scanner right on the tarmac, avoiding transport of the baggage to distant fixed installations.
Motion detection installations, like their video counterparts, are complex. When a homeowner leaves the residence, he or she enables the system by means of the central controller and disables it again the same way on returning. Computer intelligence residing in the controller manages the many devices when it is on. When different kinds of detectors (magnets, glass-break detectors, a microwave motion detection array) are used at the same site signals for all of them must be captured, integrated, and interpreted. Such systems must operate even if normal power fails as in stormy weather. Emergency power supplies are therefore important components. Modern installations can even accommodate the pet that's left behind. The family's dog wears a small transmitter that makes it immune to detection: the controller knows to ignore the dog's movements; the controller holds the necessary computing resources to manage the system and to notify the remote supervising center. That center, in turn, must have appropriate equipment to monitor the client's equipment in order to take appropriate action.
The Human Factor
Security equipment enhances our ability to see, hear, and to detect events but the equipment itself does not consciously see, hear, or detect. People must supply the meaning to the signal and weed out false alarms. Equipment is useful only when it is supervised by persons who are charged and able to take immediate action. Simple mechanical alarms that just go off and make a racket were intended to alert a responsible public or to scare off an intruder fearful that someone might show up. Too many alarms, however, may inadvertently produce the effect of crying wolf too often, as described in the children's tale about the boy who cried wolf. The frequent squeal of car alarms in a crowded city have long been an example of this phenomenon; the squealing of car alarms on a city street in the twenty-first century tends to provoke irritation rather then alarm. Similarly, when signal density is high but the supervisory staff is small, security systems lose their character as early warning systems and turn into aids to investigation after the fact provided that DVR or analog recorders captured the intrusion or the crime.
In 1969 the discovery of charge coupled devices (CCDs) at Bell Labs inaugurated digital photography. Analog signals, such as light, could now be transformed into easily manipulable digital signals. With the rapid spread of this technology, the ability to capture sharp images and to record them as 0s and 1s, gave video surveillance a great stimulus. The threat of terrorism added urgency to upgrade installations. Digital imaging holds out the promise that computers can and will take over analytical functions heretofore only people could perform. Computers could already compare fingerprints and were getting better at recognizing faces and identifying people by the patterns of their irises. Events in the first decade of the twenty-first century suggest, as strikingly illustrated by the war in Iraq, where the deployment of people is insufficient, technology alone does not suffice to stop the determined assailant. Despite that notable example, which can be multiplied by others, not least the terrorist events in the United Kingdom, notable for its massive deployment of video surveillance equipment, the betting by producers of equipment and their chief buyers is that technology will eventually trump the human element.
With the exception of alarm systems, concerning which the U.S. Bureau of the Census presents data as part of Communications Equipment Manufacturing, not elsewhere classified (NAICS 33-4290), security equipment as such is not anywhere visible in the Economic Census of the United States, conducted for years ending in 2 or 7, or in the Annual Survey of Manufactures, conducted in all other years. Data on componentry that ends up as parts of security equipment systems are, however, reported but not by end use. Consequently it is virtually impossible to piece together a picture of the total market from the most reliable data source on U.S. production, the data collected by the Census Bureau. This vacuum in information has been filled by estimates developed by market research organizations such as Freedonia Group, Inc. and International Data Corporation (IDC) and industry associations, most notably the Security Industry Association (SIA). The size of sub-markets, for instance airport security equipment, is also partially visible from budget allocations by Congress to the Transportation Security Administration.
The total market for equipment in 2006 appears to have been $13.7 billion, obtained by extrapolation of Freedonia estimates for 2003 at $10.3 billion and projections to 2008 of $16.1 billion. These data exclude revenues associated with network security products (firewalls) and sales of military equipment serving security functions. The Security Industry Association provides its own estimate of the market based on surveys of its membership. SIA reported the total market for 2006 to have been $29.5 billion, including both equipment sales and services revenues combined. From this single datum plus the estimate derived from Freedonia we infer that service revenues in 2006 were $15.8 billion, thus somewhat higher than equipment revenues. Service fees are paid monthly to bureaus that act as round-the-clock backups for residential and commercial burglar alarm installations.
Growth rates in the industry are estimated to be outperforming the economy as a whole. Freedonia's estimates for the period from 2003 to 2008 produce an annual growth rate of 9.3 percent. SIA's estimate for total revenues, reported for the 1996–2007 period, suggest growth at a rate of 8.5 percent per year. Growth in the Internet security appliance market, based on International Data Corporation numbers, is even more rapid. Revenues between 2003 and 2004, for instance, advanced at a staggering rate of 57 percent as noted in Market Share Reporter quoting IDC.
Growth in the industry is attributable to at least three factors. In computer communications the periodic outbreaks of hacker attacks stimulate bursts of investment as people, alarmed by the latest threat, review and update their software. Terrorist threats from beyond U.S. borders and outbreaks of irrational violence domestically—in the first decade of the twenty-first century manifesting particularly in violent episodes at schools and colleges—have stimulated the purchase of video and electronic article surveillance technology. Freedonia sees video systems growing most rapidly of all. Next in growth are ID/Access Control, growing 10 percent per year, stimulated by federal rules, issued in October 2006, requiring federal employees and contractors to have uniform identification credentials. Such ID-systems are typically coupled with ID-card readers to enable employees to enter facilities by unattended entrances. Thanks to the efforts of the TSA, airports were rapidly equipped with EDS and/or ETD machines in the wake of the September 11, 2001 attacks against the United States. Such systems, however, are still growing at rates greater than 7 percent a year. Lowest growth is associated with traditional alarm facilities, including residential and commercial burglar alarm installations based on motion-sensor technologies. The third factor, beyond Internet growth and well-publicized threats to public security, is improving technology, especially in the area of digital video surveillance. Freedonia attributes the rapid growth of closed circuit television systems to such improvements. Digital technologies offer more power because software approaches can be used to interpret events mechanically, lowering labor costs. Digital images are easier to analyze by computer than analog signals.
Shares of equipment classes in 2006 are presented in Figure 187. Data show that alarm and access control systems together hold more than half of the total market. Article and contraband detection, taken together, represent the bulk of airport security expenditures, approximately 11 percent of the total market; some portion of the video category, however, is also part of the airport security demand. The automotive category includes auto security devices together with systems difficult to classify into one of the other major categories.
Positive Growth, Negative Connotations
The security equipment market is a classic example of industrial development in which lower-cost machinery is intended to dis-place higher-cost and, indeed, sophisticated labor. Growth of the security equipment market, however pleasing to its producers, can only be viewed as a negative phenomenon. In other than traditional areas like warning systems, it is accompanied by intrusions into the private sphere and the slowing of commerce and travel by bottlenecks through which people and products must be sluiced for easier inspection. The category represents a social dilemma. We know how to make equipment of ever greater power and sophistication. We do not seem to know how to fix social problems, anomie, and the effect of depersonalization produced by ever increasing scales in every department of life. Mass shootings of children at a school lead to expenditures on surveillance, control equipment, and meaningless zero tolerance policies, but such expenditures and pronouncements do not appear to prevent recurrences and, indeed, the escalation of such violent events.
Three leading companies in commercial and residential security systems are General Electric, Tyco, and Honeywell. General Electric Company (GE) was a $149.7 billion corporation in 2005. GE Security Products was part of the company's industrial sector, with revenues in 2005 of $32.6 billion; of this total security products were a fraction, not detailed by the company, but GE's range of offerings is comprehensive and includes home and commercial systems, fire protection, sensing technology, access control, and video systems among others. The company offers brands under some ten trade names. Bermuda-based Tyco International, Ltd. had sales in 2006 of $40.96 billion. Its best-known brand name is DSC (for Digital Security Controls). Like GE Tyco is a leader in fire protection as well as home and commercial systems. Honeywell International Inc. groups its security systems under its Automation & Control Solutions segment, with revenues of $11.1 billion, approximately one-third of the company's total sales in 2006 of $31.4 billion. In the home and commercial security segments the company's best-known brand is Ademco. Like its competitors, Honeywell is involved in all phases of security equipment.
When charged with ensuring that all major airports were equipped with EDS systems, the Transportation Security Administration turned to The Boeing Company and Siemens USA, an element of the German Siemens A.G., to superintend the total effort. The combination has become known as the Boeing-Siemens Team. In carrying out its job, the Boeing-Siemens Team has relied on four corporations as leading suppliers of such equipment. These are InVision, an element of General Electric; L-3 Communications Corporation, a $12.5 billion corporation in 2006 predominantly active in the aerospace, defense, and government contracting segments; Thermo Fisher Scientific, Inc., a $3.8 billion corporation, selling the EGIS brand of equipments; and Smiths Group Plc., a U.K.-based corporation with 2006 revenues of £3.5 billion of which £412 million, or 12 percent, was earned selling detection equipment.
Leading companies in video surveillance equipment are Robert Bosch Gmbh, the German company, operating as Bosch Security Systems, Inc. in the United States; Panasonic Corporation of North America, a part of Matsushita Electrical Company, Ltd.; Sony Corporation, Sanyo Electric Company, Ltd., and Samsung Group of South Korea. These companies are major producers of components. Systems integration is typically accomplished by integrators who also function as distributors.
The leading supplier of network security systems is Cisco Systems, Inc. with approximately 29 percent of the world's market. The company had total sales of $28.5 billion in 2006. Other leading participants were the Finnish Nokia AB ($3.4 billion), SonicWall, Inc, of Sunnyvale, California ($175 million), Juniper Networks, Inc. ($1.4 billion) also of Sunnyvale, and the privately held Watch-Guard of Seattle, Washington. Revenue data shown are annual sales rather than revenues from network security products.
The leading company in access systems is the privately held BridgePoint Systems, Inc., located in San Leandro, California. The company is the major supplier of access card and card-reading systems to the government 874 and large institutional buyers. Two leaders in traditional sirens and fire alarm equipment are Federal Signal Corporation, with 2006 revenues of $1.2 billion and Motorola, Inc. with annual sales in 2006 of $43.9 billion. Revenue figures, again, are total, not category, sales.
MATERIALS & SUPPLY CHAIN LOGISTICS
The security equipment industry is characterized by complexity in the sense that equipment of great diversity has to be assembled at sites of future use and combined into systems locally. In effect the finished product, the security installation itself, is created at the site of its use in a process analogous to residential or industrial construction. This general characterization applies particularly to video-based systems, motion-detection installations for burglar-proofing properties, and to ID/Access Control involving electronically operated entrances and systems opened by identity cards, special keys, or devices operated by keypads. Substance detection machines are also parts of systems, but the core of the installation is machinery that comes fully assembled by the manufacturer. Automotive alarm systems, smoke-detectors sold to the public, and small kits used for monitoring babies, for instance, are more properly-speaking in the traditional product class. The nature of the equipment used has its greatest impact on the distribution channels needed to install it. From a materials point of view, most security systems rely on optical goods for video as well as motion-detection systems, communications devices, and electronics.
Residential and commercial systems are distributed as a function of providing monitoring services by a few national and a much larger number of regional and local companies. These organizations are principally in the services business. They live on subscription income from users who pay a monthly fee for monitoring services. Equipment installation is the means by which these companies obtain the ability to sell their services. Two large companies are Protection One, Inc. which installs Tyco's DSC equipment, and Honeywell's Ademco equipment. Tyco also distributes its product through its wholly-owned ADT Security Services.
Specialized wholesaler/integrators with wide lines of equipment operate as the middle-level distributors, designers, installers, and maintainers of systems for commercial and institutional customers who supervise their own systems. As illustrated by EDS equipment placed into airports, government procurement prime contractors like the Boeing-Siemens Team will operate as general integrators for the installation of systems, serving as the main channel for producers of equipment. Actual on-site work is usually subcontracted out to local firms with the technical participation of teams from the manufacturer.
Electronic network security systems are distributed through computer consultants and network integration firms. These companies handle the security aspects of systems as part of installing, modifying, and enlarging computer networks.
Among the public, users of security equipment are the wealthy or those only moderately well off but living in areas subject to burglaries. Surveillance, burglary-detection, and access systems are associated with large institutional settings of every conceivable kind. Casinos and retail stores are key customers for active surveillance equipment; in the latter years of the first decade of the twenty-first century, schools were becoming a market for such systems as well. Facilities where unauthorized entry (or exit) is most likely to cause problems, thus medical facilities, jails and prisons, government facilities, and utilities use access controls. Where valuable assets are stored owners buy security equipment to protect those assets. Police and fire protection forces are the largest buyers of warning systems. Weather systems use civil defense equipment to broadcast warning of dangerous events like approaching tornadoes. Such facilities are maintained by municipalities and other levels of government.
Markets adjacent to security equipment are services that provide traditional security using animals and humans. People and dogs, in fact, are very often associated even with quite sophisticated equipment installations. Living helpers often represent the second layer of protection, able to resolve fuzzy situations where the machines cannot produce conclusive results. Dogs are used for detecting explosives and narcotics. Human inspection of baggage and of people, with or without electronic wands, is often a necessary adjunct to screening with machines.
RESEARCH & DEVELOPMENT
In this field research and development are focused chiefly on foiling terrorism. EDS and ETS equipment are under development to detect substances more accurately and to detect more of them and faster. Integrating modularity into these systems is an important aim so that, as components are improved they can be seamlessly retrofitted with parts that deliver better performance. As inspection of cargo looms ahead as another wave in homeland protection, devices capable of providing more rapid inspections through more layers of outer surfaces are being pursued.
In the video surveillance field digital methods of image capture and analysis are still relatively new. Video sensor technologies are still rapidly developing. Lower energy consumption and higher resolution are aims. As resolutions grow, software is being modified to exploit analysis of ever sharper images capable of ever greater magnification, visual rotation, and artificially added illumination.
As the first decade of the twenty-first century was drawing to a close, developments in three areas of public or governmental concern suggest changes in the security equipment industry. The first of these is a call for a universal identification system in part stimulated by the immigration issue, in part by fear of infiltrating terrorists. Such a movement, if it gathers steam against the stout opposition of those advocating greater privacy, will probably greatly influence the form such a national ID will take. Once in place, it may lead to the introduction of ID readers on a scale heretofore difficult to imagine.
The second area of interest is pressure by law enforcement agencies to more widely install video surveillance for traffic and crowd control. This push is at least in part stimulated by the widespread deployment of such systems in the United Kingdom where such equipment is turning out to be very helpful to the police in investigating crime.
Many activists intent on securing U.S. borders are promoting expansion of goods inspection from airports to ports generally and to public ground transportation. At present Congressional funding for either thrust has been minimal. If moneys materialize, they will produce another expansion of the security equipment industry.
TARGET MARKETS & SEGMENTATION
Products of this industry are closely targeted to the nature and context of the intrusion or misbehavior that the users of the equipment intend to foil. The simplest alarm systems, including residential protection installations, are sold on the basis of modest cost and their deterrent effect. It is a reasonably documented fact that signs informing the would-be burglar that a house is protected act as a deterrent. The mere sound of a loud alarm acts to cause the criminal to slither into the shadows. At the other extreme lie threats where technical failure cannot be tolerated. Explosives detection is a case in point. In these applications equipment performance is crucially important and cost is a secondary consideration. In ensuring access control, devices difficult to counterfeit (the ID cards used) or to fool (the card readers) are emphasized for marketing purposes. In selling video systems, efficiency and flexibility are important selling points; cost-effectiveness is equally important. Systems that do more for the same basic cost—thus systems where artificial intelligence is well developed to conduct the highest levels of data analysis before summoning human help—are preferred because they permit low levels of supervisory staffing.
RELATED ASSOCIATIONS & ORGANIZATIONS
Aviation Safety & Security Association, http://www.as-sa.org/index.html
Cyber Security Industry Alliance, https://www.csialliance.org/home
Information Systems Security Association, http://www.issa.org
National Association of Security Companies, http://www.nasco.org
Security Industry Association, http://www.siaonline.org
"Airport Security Equipment Presents Strong Potential Opportunities for Investors." SecurityInfoWatch.com. 13 December 2005. Available from 〈http://www.securityinfowatch.com/online/Research—Studies-and-Whitepapers/6746SIW321〉.
"Airport Security Equipment Updates." The Boeing Company. Available from 〈http://www.boeing.com/ids/airport_security/equipment.html〉.
"Aviation Security." U.S. Centennial of Flight Commission. Available from 〈http://www.centennialofflight.gov/essay/Government_Role/security/POL18.htm〉.
"Boeing-Siemens Team Delivers Explosives Detection Equipment For Baggage Screening To 200 U.S. Airports." The Boeing Company. Press Release, 18 November 2004.
Darnay, Arsen J. and Joyce P. Simkin. Manufacturing & Distribution USA, 4th ed. Thomson Gale, 2006.
Lazich, Robert S. Market Share Reporter 2007. Thomson Gale, 2007.
"Plane Hijacking in Perspective." South Asia Analysis Group. Available from: 〈http://www.saag.org/papers2/paper103.html〉.
Stepanek, Laura. "Amid Flux, the Beat Goes On." Security Distributing & Marketing. 1 January 2007. Available from 〈http://www.sdmmag.com/CDA/Articles/Industry_Forecast〉.