Security factors
Page 8 FlexZone Product Guide
Security factors
There are many important factors to consider when planning a fence-mounted perimeter security
system:
• Fence height - The fence must be high enough to present an effective barrier to climb-over
intrusions. It should also include climb-over deterrent hardware such as barbed wire or razor
ribbon (for flexible fences). Rigid fence types should incorporate a climb over deterrent in their
design (pointed stakes or pales). Senstar recommends that the minimum fence height for a
FlexZone installation on a flexible fence type is 2.5 m (8 ft.). For rigid fence types the minimum
recommended fence height is 2 m (6.5 ft.).
• Fence condition - FlexZone detects intrusions by picking up the minute vibrations or fence
noise caused by an intrusion attempt. Therefore, the fence must be in good condition to
prevent any metal on metal contact or vibrations caused by environmental factors. It may be
necessary to upgrade the perimeter fences to ensure they present sufficient barriers against
climb over and crawl under intrusions. If you are not sure of the suitability of your fence for a
FlexZone sensor, Senstar recommends hiring a local fencing contractor to inspect, and if
required, repair the fence.
• Probability of detection (Pd) vs. nuisance alarm rate (NAR) - With a fence-mounted intrusion
detection system there is always a trade-off between the probability of detection and the
nuisance alarm rate. A properly calibrated system will provide a high Pd and will minimize the
NAR.
• Alarm assessment/response - What happens when the system triggers an alarm? Can the
alarm be assessed visually? Does the site include CCTV coverage to verify the event?
Senstar recommends engaging a security consultant to discuss the available methods of
alarm assessment. To ensure maximum confidence in the sensor you must be able to
distinguish between valid alarms and nuisance alarms.
Fence structures
To ensure consistent detection, a sensor cable should be mounted on only one type of fence. All of
the fence panels should be similar in type, size and condition. Ensure that there are no loose
panels, fittings or metal parts that can move and cause nuisance alarms. A shake test in which you
grip the fence fabric in the middle of a panel and gently shake it back and forth with an increasing
motion will help identify any loose pieces. Listen for metal-on-metal contact and correct any
problems found. Verify that there are no washouts or depressions under the fence that could allow
an intruder access. Ensure that there is no vegetation or other objects that can make contact with
the fence in windy conditions.
Note Fences that are covered with vinyl privacy slats or other screening
material may not be suitable for the FlexZone sensor due to the
vibration dampening characteristics of the screening materials, and the
additional fence motion caused by wind. It may be necessary to remove
the screening material to ensure optimal FlexZone sensor performance.
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