By CS Staff · August 6, 2008
LOS ANGELES — Running wire through a wall, drilling holes, trenching through pavement — these are just some of the not-so-pleasant tasks associated with the installation of a traditional intrusion detection system. But what if the administration at your hospital, school or university wants to avoid this hassle? Or what if your facility is unable to accommodate the wiring necessary for a burglar alarm system?
If these are your concerns, wireless intrusion detection just might be the solution for you. The use of radio-based security systems, commonly known as short-range wireless, has grown considerably during the past two decades. With the improved reliability, design and security of today’s wireless devices, campuses are seeing the benefits of being cable free. Another advantage of this kind of system is faster installation time, which can result in reduced labor costs and less downtime for a facility.
Additionally, wireless motion detectors can be installed almost anywhere. This solves a big problem when an alarm is required in an area where a wired sensor cannot be installed, such as a campus facility built on a slab with a second story above it. Older buildings such as historical landmarks or those that have aesthetics or architecture that will not withstand the installation of wired devices are also excellent candidates for radio-based intrusion alarm units. Knowing the basics of wireless intrusion devices will help you select the most appropriate equipment for your campus.
Selection of Wireless Sensors and Manual Devices Is Growing
A typical wireless system is comprised of an alarm control panel equipped with a radio receiver. In some cases, the panel is specifically designed with a receiver on board for wireless-only operation. In other cases, a wireless receiver can be added to the panel, giving the system the ability to accommodate both hardwire sensors and wireless components.
Most radio-based systems, whether wireless-only or hybrid, are designed with a full complement of wireless sensors and detectors. Just about any sensor or detector that you can connect to by using a wire you‘ll find in today’s wireless systems.
Common wireless components include motion detectors, passive and active wireless keypads, glass-breakage detectors, photoelectric smoke detectors, handheld and necklace panic buttons, single- and multiple-button panic devices, wristwatch panic buttons, single- and dual-button keyfobs, money clips, man-down transmitters, and more.
Supervised Systems Can Be Active or Passive
Most of the wireless systems sold today are supervised, which means the alarm control panel, through a connected receiver, knows which transmitters are physically and operationally in place and doing their job.
Be aware that there are two flavors of supervision available: passive and active. In a passively supervised system, the transmitters will send a trouble signal when something goes wrong. In a system that uses active supervision, each transmitter automatically sends a supervisory signal on a periodic basis. The intent is to constantly update the control panel so when something happens to a transmitter, campus security is notified.
Where automatic supervision is used, transmitters are designed to send supervisory signals every one to eight hours. If the alarm panel fails to receive a transmitter’s supervisory signal in a specific period of time, usually within eight to 24 hours, it will display the lost transmitter’s identity at the keypad. It also will automatically notify the monitoring station, which in many cases is the campus security office.
Additionally, many of the supervised systems made today will send a supervisory update to the receiver every time a change occurs in the sensor’s status. Usually included in this transmission is the condition of the transmitter battery, the status of the sensor, the transmitter identification number and any other information that the manufacturer decides is important.
There Are Pros and Cons to Both Narrow Band and Wide Band
There are two types of wireless systems on the market today: wide band and narrow band. Wide-band wireless systems are usually less expensive. Wide-band receivers “hear” a relatively wide portion of the radio spectrum. The exception to this is spread-spectrum systems, which we will touch on in a moment.
Narrow-band systems generally offer better reception when transmitters are positioned near the fringe of a system’s limit of operation. This is determined by a variety of factors, such as frequency and signal power. Proponents of narrow-band often claim these systems enjoy greater signal sensitivity because they do not have to listen to so many other radio transmissions. Detractors say that for the added benefit, narrow-band systems are not worth the additional dollars.
Proponents of wide-band technology say this type of system is more forgiving of problems in the field, such as transmitters that are slightly off frequency. Detractors of wide band say the receiver is forced to sort through a multitude of radio transmissions and that this can possibly cause it to miss a critical signal sent from a valid transmitter.
How Propagation, Frequency and Environment Interact
The successful application of short-range wireless in a campus setting requires a rudimentary knowledge of how signals are transmitted and the effects of environmental conditions on the radio signal.
Factors to consider include metallic obstructions in and about the structure; possible sources of internal or external electromagnetic interference (EMI); the equipment’s operating frequency; the specific radio technology in use; composition of structural walls and floors; and operating temperatures. All of these things can block a transmitter’s radio signal.
Electromagnetic interference (EMI) in heavy radio frequency (RF) environments can wreak havoc on short-range wireless devices. These environments include large airports; industrial facilities that use arc welders, steel smelting furnaces and noisy electric motors; and high-powered transmission equipment common to ham radio operators and those who abuse the citizens band (CB) frequencies by transmitting at higher power levels than allowed by the FCC.
To offset the effects of metallic obstructions inside a building, when installing wireless systems in large facilities or when securing a number of outside buildings that are remote from each other, repeaters and multiple receivers are sometimes used, as well as external antennas.
Spread Spectrum Offers Encryption, Security
The advantage of spread spectrum-based intrusion systems is it creates a signal that is difficult to discern and equally difficult to decrypt for would-be criminals. There are two basic types of spread spectrum in use today: frequency hopping and direct sequencing. Although spread-spectrum technology has its advantages, the high frequency band it uses is not as effective outdoors as it is indoors. This frequency band also works well in urban settings where conventional building materials are commonly used and outdoor foliage is minimal.
Don’t Be Afraid to Ask for Help, Multiple Bids
Armed with the above knowledge on wireless intrusion systems, the astute campus administrator with the help of a qualified security installer should be able to determine which wireless system is best for his or her application. When all else fails, ask several alarm firms to provide detailed bids and then sit down with each one to talk about the pros and cons of each.
Al Colombo has spent more than 30 years in various capacities of the electronic security industry.