Tech Trends: An Alternative to Traditional Door Contacts

Jan. 15, 2020
With the potential loss of Sentrol products, it may be time to reassess legacy contact technology from alarm systems

In September of this year, we received the news that Interlogix, part of UTC Climate, Controls & Security, would be permanently shut down – taking with it a number of recognizable industry brands, including Simon, IFS and Concord. If you are one of the many employees impacted by the shutdown, or one of the many alarm installers that has built a business on Interlogix intrusion panels, you have my sincere sympathies.

For many of us on the consulting side of the business, perhaps the most notable loss is the legacy Sentrol product line, which is comprised mostly of alarm system staples such as door contacts, duress buttons and glass break sensors. In particular, Sentrol had a door contact for every conceivable application – from standard hollow metal doors to a variety of surface-mount options suitable for retrofits, vaults and hatches.

I do not know for certain that another manufacturer will not pick up the line, or that warehouse stock will not be able to serve the industry in the near future, but I do know that among consulting circles, we are already looking for alternatives. Perhaps the loss of the Sentrol line provides an opportunity to look beyond traditional door contact technology.

Historically, door contacts have been based on a reed switch, which was invented in 1936 by Walter Ellwood at Bell Telephone Laboratories. A basic reed switch is comprised of two ferromagnetic magnetic contacts sealed inside of a glass envelope. In the presence of a magnetic field, the two contacts are drawn together and complete a circuit.

The basic reed switch is inexpensive and reliable under normal operating conditions – two factors which have supported its longevity as a useful tool in the security industry. However, there are also drawbacks to the reed switch, as switches – especially those based on common magnets – can be defeated by the introduction of an external magnet.

Magnasphere is one company that has developed a product line that avoids many of the common drawbacks of the traditional switch. Winner of SIA’s New Product Showcase Best in Show award back in 2002, the company is obviously not new to the industry. Over the years, Magnasphere has built a loyal following and increasingly large install base.

A Closer Look at Magnasphere’s Switches

I had an opportunity to connect with Michael Keegan, VP of Security Products at Magnasphere, recently at our office. “The technology inside the vast majority of door position switches/door contacts is the reed switch, which is protecting millions of doors throughout the world even though it breaks easily, fuses from voltage spikes and is easy to defeat,” Keegan says. “Invented in the 1930s this reed switch technology has continued to be utilized because there has never been a significant improvement for protecting doors and windows. The Magnasphere switch is that improvement. The patented and award-winning switch addresses all the vulnerabilities of the reed switch…(it) doesn’t break, it doesn’t fuse, and it is defeat resistant.”

The switch technology is based on a small magnetic sphere (hence “Magnasphere”), which is placed inside a metal housing. In the absence of an external field, the ball is drawn to one end of the housing. When a companion magnet is placed in a small activation zone adjacent to the housing, the ball is drawn to the other end of the housing, where it completes a circuit. The activation zone is restricted to a small area directly adjacent to the housing.

This is a substantial improvement over a reed switch, which has a larger activation zone that often extends outside of the door or window frame, allowing it to be defeated by an external magnet.

UL-634 is the oft-referenced standard for connectors and switches for use with alarm systems. Levels I and II describe switches that have higher levels of defeat resistance and tamper protection. According to Keegan, many of the terms historically used to describe high security door contacts are now outdated. “When designing a security or access control system or specifying door protection, terms like ‘high security’ or ‘balanced magnetic switch (BMS)’ are no longer relevant,” he says. “Reference to the UL-634 standard is the only way to get the proper level of detection and tamper supervision installed.”

The Magnasphere product, due to its higher level of defeat resistance, has gained particular traction with government and military applications. The company’s contact products meet UL-634, and high-security lines meet the more stringent UL-634 levels I and II.

Maintaining fire rating is another important consideration. “It is also important to note, and often overlooked, when fire-rated doors are protected, they must have UL-10C classified door contacts installed,” Keegan says. “Magnasphere, because of its robust construction, has a number of models that meet this stringent standard. Some are classified for as long as three hours.”

Magnasphere has published a convenient listing of direct replacements for Interlogix/Sentrol door contacts, which is available on its website at

Brian Coulombe is Principal and Director of Operations at DVS, a division of Ross & Baruzzini. Contact him at [email protected], through Linked in at, or on Twitter @DVS_RB.