NOT LONG AGO, indoor intrusion detection technology could only indicate whether a door had been opened, a window had been broken, or a warm body inhabited a room. Continuing technological advancement has enhanced the reporting capabilities of these systems, and now the creative security manager and system designer can use the technology to solve problems beyond a system ‘s original purpose.

A typical door/window intrusion sensor, for example, can also be attached to a variety of other items that open and close, such as cabinets, drawers, display cases, and room dividers. Recently, when a Las Vegas casino began suffering heavy thefts from its vending machines, the security manager placed wireless door/window sensors on the machines’ locked cash box doors. Because sensors reported the machine’s identity, location, and operating status to the control panel and, hence, to human monitors, when the thief struck again, he was easily apprehended.

A security manager asked to install interior intrusion detection must decide what sensor technology will best fit the application. Factors to consider include the following:

• What is to be sensed-for example, an open or shut door or window, motion, heat, power on/off, an exact temperature or range, or glass breaking? That will determine the sensing technology, which could be: passive infrared, microwave, glass-break, or magnetic.
• Where will the sensor be placed-on a door or window, for instance? Will the sensor be permanent? Will the signal have far to travel? Will aesthetics be important? The answers to these questions will determine the sensor type and other factors, such as how the signal should be sent: over hardwire or by wireless radio frequency (RF) transmission.

Motion sensors are the most difficult type to place due to the Importance of preventing false alarms.

Technology Types. Among popular interior intrusion sensors, as mentioned, are motion detector (microwave or passive infrared), glass-break, and magnetic.

Motion detector: The most common single-technology motion detecting sensor uses passive infrared (PIR) energy to recognize the movement of heat in a protected space, such as a person walking across a room. It is most effective in detecting when the heat mass moves across its field of vision. Dual-technology motion detecting sensors employ PIR and microwave technologies. Both must activate to signal the control panel, thus false alarms.

Motion sensors are the most difficult type to place due to the importance of preventing false alarms. Considerations for motion sensor placement include sources of ambient temperature changes such as heating vents; sources of movement such as pets, wind, and normal traffic patterns; and sources of light such as automobile headlights.

Motion sensors are wall-mounted. A 360-degree motion sensor can be placed on the ceiling and is especially useful in schools, colleges, nurseries, churches, libraries, and other areas where tampering is a concern. The ceiling-mount is also designed for warehouses and other storage areas where the view of a wall-mounted PIR may be obstructed.

Like a radar system, the microwave motion detector emits energy and analyzes it by measuring the different frequencies of the returning microwaves as they bounce off the moving object in question. Microwave sensors are most effective in detecting objects moving toward the sensor rather than across its field of vision.

Microwave sensors are especially effective in harsh environments where heat sources cycle on and off, and where PIR technology might be prone to false alarms from heating vents, for example. The sensors are also commonly installed in large storage spaces like warehouses where the air flow is difficult to control.

Glass-break sensors: Another type of interior sensor relies on the sound and aftershock of breaking glass to trigger an intrusion alarm. These glassbreak sensors monitor windows, glass doors, and skylights, and come in three varieties: shock, acoustic, and combination technology.

Shock sensors register the shock frequency of breaking glass. Surface-mounted glass-break detectors are mounted on the glass itself with an adhesive. They are often installed on large picture windows and in businesses with large storefront windows. The combination sensor must both register the shock and hear the specific frequencies of breaking glass before signaling an alarm.

A unique use for shock sensors has been devised and put to the test by Connie Higginbotham of Security Services, Inc., in Rocky Mount, Virginia. According to Higginbotham, she uses the sensor as part of a vehicle alert system. The sensor activates by a pneumonic tube placed across a driveway or road, similar to the tubes that ring bells at service stations. When a vehicle driving over the rubber hose increases air pressure inside the hose, the pressure activates a diaphragm with a frequency detectable by a shock sensor of the appropriate sensitivity.

When armed for local annunciation only, the driveway sensor activates a chime that announces the arrival of customers at car lots, mobile home parks, and rental storage facilities, as well as the arrival of trucks at commercial establishments. When used as part of a monitored security system, the sensor detects the presence of unauthorized vehicles and sounds an alarm. In one of Higginbotham’s applications, the system prevents the theft of boats and trailers from an outdoor storage area.

Magnetic sensors. Magnetic technology is the basis of door/window sensors. These sensors identify intruders by using a magnet and reed switch mechanism. The reed switches are electrical contacts held open by the presence of a magnet. When a magnet attached to an opening door moves away from the reed switches in the alarmed sensor, the switches make contact with each other and trigger a radio frequency (RF) transmission to the system control panel. Information in the RF transmission identifies the type and location of the sensor.

Door/window sensors can be surface-mounted or recessed. Wireless recessed sensors fit inside holes drilled down into the top of the door and up into the doorjamb so that the reed switch and magnets are hidden from view. The magnet is generally placed on the moving door and the switches on the stationary doorframe. They are held in place by screwed-in bases or double-sided adhesive. The manufacturer’s recommended range to a control panel will vary, depending on whether the signal is sent by wire or wireless means.

WIRED. Indoor intrusion sensors come in wireless or hardwire versions. Hardwire sensors transmit information via wired circuits; wireless sensors communicate via RF transmissions. Each type has advantages and disadvantages.

Hardwire sensors are, on average, less expensive. However, savings from hardwire sensors may be offset by increased installation costs to run wire from the sensor to the control panel.

Wireless is less intrusive and, obviously, allows more flexibility in positioning sensors during installation and repositioning should the need arise, such as when the use of a space is altered and requires a change in security. They also take less time to install than hardwired sensors.

Wireless sensors are powered by batteries. Supervised wireless systems report the identity and battery status of each sensor at regular intervals, so system users know that components are operating properly. Lithium batteries in intrusion sensors are replaced about every five to eight years. One door/window sensor on the market today comes with a battery expected to live twenty years, ten years of which are guaranteed by the manufacturer.

An application in which a hardwire system would be preferable might be interior areas not slated for any foreseeable renovation or that house permanent collections. Another would be a large, permanent structure-for instance, a warehouse-in which many sensors will be used. In this case, hardwiring the sensors would avoid a massive battery replacement program.

Sensor selection is sometimes determined by environment, cost, or aesthetic preferences. Aesthetics play an especially important role in sensor selection when the historic quality of the protected area is of value. The advantages of wireless sensors in such settings include a less intrusive and less potentially damaging installation.

Ideal applications for wireless sensor systems include buildings where the end-user plans to move the system to a new location, historic landmarks where preserving the structures as built is vital, sites that are intermittently occupied, and renovation projects where wireless sensors can protect the building and tools from vandalism or theft. At one construction site, for example, a pile of lumber was fitted with a wireless door/window sensor that sounded an alarm if the pile was disturbed. Sensors can also be discreetly fitted on toolboxes and construction equipment.

Wireless sensors were also chosen for use in the historic, ten-story Walnuts condominium complex in Kansas City, Missouri, to avoid potential damage to ornate wooden molding valued at $l million. Yet another example is the North Carolina Museum of History in Raleigh, North Carolina, where the museum’s galleries change in size and configuration to fit the needs of special exhibits.
“You can have a space that’s a few hundred square feet one day and a few thousand square feet the next,” explains Jimmy Ray, director of security at the museum. “When gallery layouts change, wireless intrusion sensors can be rearranged economically and unobtrusively, without disruption to normal museum activities.”

Often, it is not an either/or decision but rather a blending of technologies to suit the diverse needs of a site. Ray says that the entire building’s electronic intrusion detection system is a compatible combination of wireless and hardwire technologies. The static section of the museum is hardwired and controlled from the same keyboard and control terminal as the wireless system used for the galleries. The arrangement eliminates confusion and inconvenience that would occur with separate controls.

A common misconception among security managers-one that is founded on experiences with old wireless systems–is that all wireless systems have range limitations that make them unsuitable for commercial applications. Old single-antenna, wide-band systems were unable to transmit over long distances because single-antenna receivers missed signals, and excessive noise was caused by wide-band transmissions. New receivers with dual spatial diversity antennas pick up signals missed by old systems. Narrow-band transmitters and the surface-mount technology of new receivers combine to create a communications system that uses RF energy more efficiently and produces stronger signals with longer range.

Consequently, long distances between sensors and the control panel, or glass-enclosed areas, can now be monitored successfully with a wireless system. For example, the greenhouse at the Biltmore Estate in Asheville, North Carolina, is a glass-roofed conservatory where plants are grown for display throughout the house and gardens of the estate. A smaller greenhouse four hundred feet away is similarly monitored and reports to the same control panel.

“Wireless [sensors were] part of our initial design for several reasons,” explains security system installer Kirk Saunders of Asheville Security Systems. “The greenhouse is slated for major renovation and that would have meant serious headaches for us down the road. We installed the whole system and now can remove individual sensors easily. If the cactus room is the first area to be renovated, we can remove the sensors and delete them from the system and leave the rest of the spaces alone. And we don’t even think about range anymore. It’s not ‘will the wireless signal reach?’ but, ‘which system design will get us the distance we need this time?”‘

New Applications. Door/window sensors are the most commonly selected type of indoor intrusion sensor for portal protection, but they can be used to do much more. The sensors can also, for example, be wired to a variety of measuring devices to alarm in the event of high or low temperature.

At the Biltmore Estate’s conservatory and greenhouse, temperature control is critical throughout the year, especially when the conservatory nurtures the thousands of poinsettias used to decorate the house for annual Christmas celebrations. Temperature monitoring is achieved by wiring electronic thermometers to wireless door/window sensors to take advantage of the sensor’s reporting ability. When the thermometer needle reaches the low set-point indicator on the thermometer, an electrical circuit is completed and detected by the door/window sensor, which activates a security system alarm.

Other uses for the modified sensor include monitoring temperature variations to prevent losses due to frozen and burst pipes, setting sensors to alarm for high temperatures that can kill livestock or damage inventory, or monitoring low temperatures that can damage crops or other vegetation. Sensors have also been wired to meters at sewage treatment plants to warn when effluent levels threaten to contaminate ground water.

Panic attack. Another application for interior intrusion detection is the use of wireless portable panic buttons. The buttons are worn by a facility’s staff or security force and are programmed with unique identification codes, just as a mounted door/window sensor might be.

The specific codes of each panic button correspond to specific areas within a monitored facility. An activated panic button assigned to a security officer who has detected or suspects an intrusion will inform security staff of the alarm’s area of origination. Although the wireless signal does not pinpoint the exact physical location of an emergency, it does indicate the general area of the alarm. In addition, it saves time for security personnel wearing the button compared to having to get to a panic button at a fixed location.

For example, according to the North Carolina Museum of History’s Ray, it was decided that workers in the museum’s offices should carry panic buttons as a way to signal an intruder or duress alarm and activate a communicator that will summon police. This same technology has already been adapted to allow the elderly and others to signal for assistance by pressing panic buttons they wear as pendants. Employees carry the buttons on their person or wear them on neck straps. The portable panic buttons are also used by security guards who walk the closed facility.

Portable panic button applications include banks, museums, and hospitals. Although wireless sensors and panic buttons cannot be used in environments that block signal transmissions, it is by no means clear which environments those are without testing. It is a mistake, for example, to assume that a hospital or airport cannot be equipped with wireless security devices because of x-ray machines or radio communications equipment. Signal tests in many areas of airports and hospitals show normal strength and reliability in spite of the presence of other RF sources. Complex sensor signal encoding and receiver decoding technology discriminate among various frequencies to achieve reliable communication.

Keeping track. Intrusion detection sensors not only signal the presence of an intruder, but sensors can also, when tied with card access, bar coding, or other tracking technology, signal movement of assets or personnel. A time and attendance record can be developed, including the times of day when employees enter or exit, and the times when they arm or disarm the security system. In one recent case, a company employing a worker suspected of chronic tardiness used the system to track and document when the employee actually arrived. In retail situations, systems have been used to prove that store opening and closing times are being adhered to.

What’s Ahead? Indoor intrusion protection sensor technology will continue to become more and more flexible in hardwire and wireless compatibility among components made by different manufacturers. Components will also become smaller in size, and their cost will continue to go down as more efficient manufacturing methods are perfected.

All of these improvements will allow security practitioners and system designers to make good use of the technology for ever-broadening purposes.

Reprinted from Security Management © American Society for Industrial Security, Alexandria, VA. All rights reserved.