Security Factors; Fence Structures - Interlogix FlexZone Series Product Manual

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). The recommended minimum fence height for a FlexZone installation
on a flexible fence type is 2.5 m. For rigid fence types the minimum
recommended fence height is 2 m.
• 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, it is recommended 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? It is recommended to engage 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, one 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 anyproblems 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.
FlexZone™ Product Guide
Chapter 1: System planning
3