Nuisance alarms are typically caused by people, animals, insects, moving objects, improper hardware selection, placement, adjustment or application. This article will focus on hardware selection and application and for purists, adjustment.
I would be remiss in a discussion regarding hardware selection and nuisance alarms without addressing the long-lived passive infrared motion detector, or PIR. They have been a burglar alarm staple for decades, a device to sense occupancy to trigger HVAC systems and lighting and they see regular duty as a request to exit device in access control systems. When deployed in a burglar alarm and/or access control environment, they can be the source of many nuisance alarms.
As with many sources of nuisance alarms, it isn’t the actual PIR that is the culprit. In access control applications, the sensor may not be aimed properly or perhaps the reaction/sense time isn’t quite right. There is a human factor that can’t be ignored as well. “The lingering goodbye alarm” is a classic example. Someone is leaving a room or building, and stops at the door to carry on an extended conversation, perhaps some last minute instructions or a “lingering goodbye” to a colleague. The motion sensing request to exit or REX device is no longer sensing motion as this chatty person is lingering beneath it. The conversation ends, the door is opened, the magnetic contact switch senses the door opening prior to the REX sensing motion and a door forced alarm is generated. The motion sensing REX as doing its job as best it can.
With existing installations, once the aiming and timing have been checked, the only practical no-cost solution is training users not to linger while leaving an area. My best practices call for a sounder, appropriate for the application, and they are typically placed directly above the spot where the “lingering goodbye” takes place. In the case of a very loud piezoelectric sounder, the sounder itself may be the training medium.
My choice for most new installations (existing applications as well) is to deploy a REX switch that is integral to the door hardware, typically in the form of an electrically operated lever-set or retractable panic device. Since this type of installation requires an electric transfer hinge or similar device to connect to the lever-set, it’s most practical to add the additional hardware and wiring to accommodate more than a simple REX switch. It may also be time to consider a latch bolt monitor as well, to catch cases of duct taped latches and other workarounds.
I’ve introduced yet another source for a nuisance alarm, as if the timing isn’t adjusted properly, the latch bolt monitor can become a frequent source of alarms. The “lingering goodbye” can come into play in this installation as well, for example, if the converser holds the lever down for an extended period of time, and then opens the door, there’s another nuisance alarm.
Regarding existing installations, windows are a potential weakness in many access control and even some burglar alarm applications. Window alarms employ a simple electric circuit. Break the window, which breaks the wire, which breaks the circuit and an alarm activates. The industry has advanced to include sensors placed on the windows to the now commonplace glass breakage sensor placed inside a secure area. The device responds to the compression of air caused by a breaking window, along with a sensing of the actual frequency of the sound of breaking glass. Often, a PIR motion detector will be placed in the secure area to detect intruders that enter via a window or hide in an area until after hours.
Not all access control systems are deployed with burglar alarm type features, unfortunately. They’re often thought of as an enhanced lock with an audit trail.
Are you experiencing an increase in crime at your facilities? First, take note of your existing resources. You may find that you already have devices in your system that can be “assigned” multiple tasks. It may be a matter of a software purchase or adding additional licenses. This is where I often consider seeking additional resources to review existing systems. I may utilize internal staff, security consultants, or a security integrator. Frontline security officers and system monitors often provide fresh ideas for utilizing existing resources, changes in procedures and suggestions for future purchases, if they are asked. They are also a great source to learn of nuisance alarms that are not being reported, or minor changes and improvements in physical security that have fallen off of your radar.
Be sure to assess all of your existing tools on a regular basis. Chart the number of nuisance alarms that officers are responding to. Replacing a few traditional PIR motion sensors with an IP video solution may pay for themselves by an increase in resources that results when nuisance alarms are reduced. If your nuisance alarms are an extensive diversion to your core mission, you might consider a more formal ROI study. You might be surprised that you can still do more with what you have, and hopefully, before you are forced to do so.