The Starting Defense

The first line of defense in any type of security starts with perimeter detection; what better way to achieve effective protection than through the deployment of magnetic contacts and sensors? These workhorses of security have advanced like other products, but some have changed more than others simply due to their composition.

In the case of magnetic contacts, the technology is constant, but the devices have become smaller, more reliable and able to operate in a variety of environments and conditions. In intrusion detection sensors, new microprocessor developments and special imaging capabilities and processes equal intelligent and smart detection. Upon powering up, some sensors automatically adjust to the environment they are protecting and select the optimum operating mode. They continually monitor their surroundings and include redundant supervision and the ability to catch real alarms but thwart false or nuisance ones. Environmental disturbances are no problem, as these detectors have higher thresholds of tolerability and compensation.

In an integrated environment, these devices have their place. Not only do they warn of a security breach when a signal is sent to an alarm panel, but they can also shut down or start heating, ventilating and air-conditioning systems; activate lights in the case of occupancy sensors; alert a guard; or turn on surveillance cameras.

Contacts and switches
Magnetic switches, contacts and roller plungers serve well in protecting windows, doors and other entrances, including sliding patio products and even steel, overhead or curtain-type doors. They come in surface mount, recessed devices and special purpose units, which may be housed in armored cable or double or triple biased for higher security applications.

Contacts come in different operating specifications/switch configurations: closed loop—switch closed when magnet is in proximity; open loop—switch open when the magnet is in proximity; single pole, double throw (SPDT)—switch has common, open and closed sides; and double pole, double throw (DPDT)—two switches, each having common, open and closed sides.

Suggested applications for magnetic contacts include protecting a freezer door against unauthorized entry, security revolving doors, hinged skylights and roof hatches, drop-down stairs, arming cash register drawers with bill traps, and deployment on trucks and trailers at loading docks as well as truck tailgates, and fences and gates.

Sensing technologies
Passive infrared (PIR), microwave and dual technology units that combine two different sensing technologies are also part of the starting lineup of security defense. For the residential customer, they’ve become smaller and less obtrusive.

PIRs are sensitive to moving, heat-emitting sources. Dual technology devices, such as combination PIR and stereo Doppler Microwave, must both trigger within a certain threshold of time and under specific operating conditions. Dual-element PIRs have two elements or sensing heads that must trigger in order to activate an alarm.

Because of the impact of false alarms and with authorities threatening non-response or hefty fines, manufacturers have begun to continually refine sensors and detectors. For example, units that create special thoroughfares or “alleys” for smaller creatures such as pets and even rodents are standard. Onboard sensitivity controls and adjustments allow the installer to fine-tune the product to the application.

Glass break (acoustic and shock) detectors present another viable method of intrusion detection. Devices that combine audio- and shock-measuring characteristics respond if they detect the sound and vibration energy from breaking glass (or someone pounding on the glazing).

Shock sensors feel the vibration of mechanical energy passing through the glass, wood or other framing material. These sensors are usually mounted on glass but in some cases can be window-frame-mounted.

Don’t forget pull switches, panic devices, bill traps, water temperature sensors and others in your arsenal of physical protection. Manufacturers and distributors will be able to provide you with the best product for the application.

Sensors and detectors represent additional ways to sell upgrades or additional coverage to your existing or new customers, especially when you can suggest scenarios they may face.      EC

O’MARA is the president of DLO Communications in Park Ridge, Ill., specializing in low-voltage. She can be reached at 847.384.1916 or



About the Author

Deborah L. O'Mara

Freelance Writer
Deborah L. O’Mara is a journalist with more than two decades experience writing about security, life safety and systems integration, and she is the managing director of DLO Communications in Chicago. She can be reached at

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