Intrusion Detection Can Work Magic

There is certainly more science than hocus pocus involved in maximizing the accuracy and value of an intrusion alarm system. However, a high level of skill is required for a successful technician or magician, and proper use of sensors and installation methods can produce results no less amazing.

This month we are going to take a comprehensive look at some popular intrusion sensors and the installation techniques that are critical for an alarm system to perform reliably. Failing to keep track of the performance parameters of different types of detection devices can lead to false alarms, detection misses, and overall lack of confidence from users and local law enforcement. Read on for some tricks of the trade.

Base Design on ‘5 Ds’ of Security

Even a basic alarm system should be designed with specific layers of security. This should consist of both physical and electronic security components. Select a strategy in which layers of security are defined. What is the perimeter of each area and what are the higher risk areas in the home or facility? Remember that every room has six sides, not just four. 

Do you remember “The 5 Ds” of a good security system (Deter, Delay, Deny, Detect and Dispatch)? What is the true perimeter of each area? How much does the customer want to spend to extend their detection zones for the earliest possible warning?

With the advent of remotely controlled electronic door locks I have noticed the beginning of a new security trend, even in home alarm systems. We now have the potential when a system is armed the doors are automatically locked; when a door is locked, the alarm is armed; and if an intruder is detected at the outer perimeter the access doors are immediately locked. (See this month’s Tool Tip box.)

Sensor & Installation Guidelines

Through the years I have written several “Tech Talk” columns about specific intrusion sensors. Let’s review some of the key installation and application guidelines for different intrusion sensors.

Acoustical Glass Break (AGB) — These devices detect the unique sound patterns that breaking glass generates.

Follow manufacturer’s instructions closely. An example would be that some allow for AGB devices mounted next to windows, others facing windows.

  • Use the correct tester as it was designed to test the specific AGB.
  • Do a final test after carpets, draperies and furniture have been installed. They can substantially affect AGB performance.
  • Select the correct AGB sensor and settings for the type of glass being protected.
  • Positioning an AGB too close to glass can create false alarms. Something as simple as tapping a quarter on the glass can trip some AGB detectors. You may want to look at ¾-inch of maximum range with tester and furnishings in place. Additionally, placing an AGB very close to large windows may cause a saturation of the detection circuit on some AGB sensors and a possible missed alarm.
  • Does the customer have a way to accurately test their AGB devices?

Motion Sensors — Unless otherwise mentioned we will be talking about passive infrared (PIR); however, microwave can come in handy at times.

  • Place PIR in a high traffic area that is facing inward and not looking at changing heat sources, such as AC/ heating vents and windows.
  • PIRs are more sensitive to movement across a detection area and not approaching the PIR.
  • Use pulse count settings for false alarm reduction with caution as too many counts in certain locations may result in areas not being protected.
  • Make sure to seal PIR cable access openings to reduce bug penetration and false alarms.
  • Place bug strips or spray nondestructive bug spray on a sponge piece and place in PIR. Spray area around PIR with bug spray in commercial and outdoor areas.
  • Use dual-technology motion devices such as microwave/PIR to reduce false alarms. Wire or program cross-zoning of two similar or different devices to reduce false alarms in a particular area. (Suggestion: You might want to reference the previously reviewed Dolph Double Trap circuit for motions that have form C relays;
  • Wire the tamper switch and put EOL (end-of-line) resistors in device. Consider PIR models with masking tamper supervision for commercial accounts.

Overall Installation Tips — Knowing a few basic installation guidelines can help with installing reliable intrusion systems.

  • Make sure cable runs are at a right angle to AC line voltage runs. Running cables parallel can cause interference on alarm cable runs due to a coupling effect.
  • Leave a loop in the cable in your terminations as you never know when you have to make a slight adjustment.
  • Make sure to use plenum-rated cable in ceiling areas that are considered an air return space.
  • Keep a log in your alarm panel identifying all cable runs, location of splice boxes and EOL devices. Log all service visits.
  • Make sure customer understands all operations and functioning of alarm system.

Properly Terminating EOL Loops

Recently, a “Tech Talk” reader reminded me of an installation question that often gets overlooked. Thanks to Jim Sutton of AAA Alarm Systems Ltd. in Winnipeg, Canada, for this timely inquiry on EOL loop supervision.

If a tech is to take the time to install EOL supervision, then the EOL resistors should be placed at the end of the alarm loop. There is often confusion on the correct placement of normally closed (N.C.) series alarm contacts.

Note that they should be placed in series on the nongrounded side of the alarm loop. Possible shorting of an alarm loop will most likely be from a ground to alarm loop cable conductor. This could simply be from cable rubbing a sharp metal edge on a conduit or a misplaced staple. Typically the alarm loop common connection is ground.

An alarm loop has a better chance of supervising shorts by placing the NC alarm contacts on the hot side of the alarm loop (see diagram).

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About the Author


Bob is currently a Security Sales & Integration "Tech Talk" columnist and a contributing technical writer. Bob installed his first DIY home intercom system at the age of 13, and formally started his technology career as a Navy communication electronics technician during the Vietnam War. He then attended the Milwaukee School of Engineering and went on to complete a Security Management program at Milwaukee Area Technical College. Since 1976, Bob has served in a variety of technical, training and project management positions with organizations such ADT, Rollins, National Guardian, Lockheed Martin, American Alarm Supply, Sonitrol and Ingersoll Rand. Early in his career, Bob started and operated his own alarm dealership. He has also served as treasurer of the Wisconsin Burglar and Fire Alarm Association and on Security Industry Association (SIA) standards committees. Bob also provides media and training consulting to the security industry.

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