Showing posts with label Chain link fences and false alarms. Show all posts
Showing posts with label Chain link fences and false alarms. Show all posts

Friday, February 27, 2015

Q&A: Chain Link Fences and False Alarms

We're having false trips on an outside chain-link fence about once every two days. Can you advise us on possible causes and how to fix it?

It’s not uncommon for chain link fences to become susceptible to false alarms over the years for a variety of reasons. Before we go into the possible answers, let’s discuss how these barriers are commonly protected and what kinds of environmental conditions will affect the quality of use.

There are many ways to protect a chain link fence. Common methods include vibration sensors mounted on the fence fabric, metallic and fiber-optic cable designed to detect movement no matter how minute, light-of-site products that install inside the fence line, as well as several others that rely on either mechanical or electromagnetic disturbances of the wire mesh.

Most of the fence alarm systems mentioned above are susceptible to false alarms by a number of sources that usually boil down to a poorly maintained fence line. Probably the most common problem is that of excessive growth of foliage along fence lines. Trees with limbs that make contact with fences are especially troublesome during high winds. The other problem is torn fence fabric. The cure for all of these is to simply maintain your fence line.

With that said vibration sensors can require adjusting as they age. Adjustments in some systems must be done at the sensor while in others it’s performed in the main processor, usually by adjusting the detection threshold. In older devices this is performed using a small trim potentiometer on the processor circuit board. In newer systems sensor threshold adjustments is performed in software.

Probably the most false alarm-free detection technology is that of the taut-wire fence systems. The most common type mount atop the fence as well as at intervals along the fence line in a horizontal manner. These are spring-loaded, sensor-driven systems that require a more positive and verifiable means of detection. But like their on-fence sensor counterpart, you may have to tweak one or two sensors in a taunt-wire system over years of use.

If you have additional questions, or if the answer provided did not cover your specific application, please send an email with your situation and question to

John Larkin, Senior Partner