A Breakthrough in Alarm Switches
For the first time in decades, innovation is rocking the world of intrusion contacts. Discover how new alarm switch technology may make established drawbacks like fragile construction, global activation, fusion susceptibility and magnetic manipulation a thing of the past.
It’s doubtful Walter Ellwood had any idea his invention in 1936 would be the most commonly used component of a security system. It was 75 years ago when this Bell Telephone employee patented what we all refer to as the reed switch. While this device has become an industry staple, it has a number of shortcomings when used for intrusion alarm applications.
These issues have the potential to create liability for security dealers and risks for customers. When a reed switch fails, because it is wired in a normally closed configuration, the alarm control sees that zone as normal. That door or window may allow an intruder access to your client’s home or business undetected. Regardless of your insurance and contract protection, an undetected break-in is a public relations nightmare.
Fortunately, following an extended period without much in the way of change, improvement or innovation, a new approach to alarm contact design has emerged. Following is a look at the development of the alarm switch, from its beginnings to present day and its apparent future.
A Historical Perspective
Let’s begin by reviewing what a reed switch is, how it operates and the origins of its technology.
The reed switch is an electrical switch operated by an applied magnetic field. It consists of a pair of contacts on ferrous metal reeds in a hermetically sealed glass envelope. The contacts may be normally open, closing when a magnetic field is present, or normally closed and opening when a magnetic field is applied. In the alarm industry, the reed switch is used in door and window contacts and is operated by bringing a magnet near to the switch. Once the magnet is pulled away from the switch, the reed switch will go back to its original position.
It was not the first technology used for detecting door and window contacts, not by a long shot. In fact, you have to go back to 1852 when Augustus Pope fi led U.S. patent No. 9802. In William Greer’s “A History of Alarm Security,” he writes that to protect doors and windows, “Pope designed simple magnetic contacts. They consisted of a metal plate, attached to the door or window frame, and a spring and pin that was secured to the windows and doors themselves. He wired the contacts in a series circuit, running the wire around a U-shaped metal bar to form an electromagnet.”
Numerous contact patents have been filed since Pope’s. The most significant impact these patents made on the alarm industry began in the late 1970s. Until then, the favored security contact was the mechanical magnetic contact switch – primarily plunger style or the roller plunger recessed into door frames and a larger, surface mount style. These mechanical switches would make a “snap” sound when activated by the magnet or when depressed by the door closing. The current traveling through this circuit kept the contact points clean as the door opened and closed.
A typical problem of the contact in this mechanical switch era was the device sticking or freezing in the closed position. This was especially common in doors and windows that were not often used. The door contact would not be exercised and the contact points would stick. This entry point would remain inoperable until it was discovered by the system owner or when an inspection was performed. A simple tap of a screw driver was often all it took to get the door functioning again.
Reed Switch Rules the Roost
As the 1970s drew to a close, the alarm industry saw the emergence of solid state-based control panels. This allowed a smaller reed switch to be used as the basis for the magnetic contact. The race was on as an increasing number of manufacturers utilizing the reed switch created an ever-expanding line of contacts that were smaller, more specific to door and window styles and in multiple colors. This continued for some 30 years.
While the reed switch remained virtually unchanged, much of the industry’s technology surrounding it continued to evolve. For example, the time-lapse VCR was invented and replaced by a DVR. The DVR then lost market share to the NVR and now, network cloud computing looms to make even the NVR a thing of the past. In 1980, the ultrasonic detector was state of the art before being replaced by the photoelectric beam, the passive infrared (PIR), dual technology and pet immunity.
All that while millions of reed switch-based contacts were installed. And it has done so despite some well known and accepted shortcomings:
- When a reed switch is exposed to voltage, it will fuse and fail
- When a door swells from temperature changes, the recessed reed switch can be squeezed and fail
- Since a reed switch is enclosed in glass, improper handling in transportation or in installation will break the glass and cause the reed switch to fail
- When an additional magnet is presented near the reed switch, the reed will hold closed and be inoperable when the door or window is opened
In more recent times, an alternative has surfaced that offers the promise of eliminating many of the trappings of traditional reed switches while bringing alarm contacts more inline with present-day technology. The breakthrough came from a curious and ingenious man named Dr. Randall Woods, who studied electrical engineering before eventually becoming an ophthalmologist.
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