Principles for Intrusion Detection
A security system is only as good as its weakest link
- By Pete Accetturo
- Feb 01, 2012
The best defense is a good offense. That often-used sports principle
applies to military applications. It is an axiom that applies to the security
industry, as well. When it comes to perimeter security, though,
a strong offense provides a good defense, but that defense will be
only as strong as its weakest link. The question to be answered is how
good is that defense? Or where is the weakest link?
If there are weak links, then you have unprotected perimeters, which means unprotected
assets, unprotected people and, inevitably, security breaches. The ramifications
of these breaches can be disastrous, so the threat of intrusion remains a
prime concern at all facilities. Because many perimeters are simply too long for
conventional security patrols to cover practically or effectively, advanced perimeter
intrusion detection systems (PIDS) have become the only answer.
Historically, PIDS have had some trouble clarifying between a true positive and
a false positive (nuisance alarms). All too few PIDS provide sufficient analytical
tracking, real-time assessment or any environmental capability, making it extremely
difficult for security officers to respond to the ingress or egress point in a prompt
manner. Technology has advanced to the point of offering a wide array of sensing
solutions for PIDS. Those PID solutions come with an array of efficiency, costeffectiveness
and precision. There are some important factors to consider when
reviewing current PID technologies:
- System durability/reliability;
- Minimal nuisance alarms (false positives)
- Maximum detection capability;
- Minimal maintenance
- Ability to accurately pinpoint the location of intrusion; and
- Ability to work with other/complementary technologies.
Since the dawn of civilization, maintaining perimeter security has been a top
priority. Having some form of it—whether a city wall, a moat or even trained
animals—has always been critical for stopping, delaying or deterring a perimeter
breach. Even with primitive perimeter security systems, having real-time intelligence
and immediate response is vital. The difference between being aware of a
breach and the intelligence to properly respond can truly mean life or death.
While technology has advanced over the years, the security fundamentals have
not. Today we have both active and passive intrusion detection technology. Video
analytics; sonic, infrared, radar and fiber optic sensing; and buried vibration and
sonic or attenuation detection all have significant roles in PIDS. Fundamentally, good physical security is a combination
of four defensive principles: deterrence,
delay, detection and denying a breach.
The first two actions are considered
passive defense while the latter two are
active in nature.
The goal of physical security is to convince
potential attackers that the likely
costs of attack exceed the value of making
the attack (e.g., that consequences
of a failed attack may well exceed the
gain). The combination of layered security
features establishes the presence
of a security-rich deterrence system.
The initial layer of security for
a campus, building, office, or other
physical space uses crime prevention
through environmental design to deter
threats. Some of the most common
examples are also the most basic—
warning signs, fences, vehicle barriers,
vehicle height-restrictors, restricted
access points, site lighting and trenches.
However, even passive things such
as hedgerows may be sufficient in some
The next layer is mechanical and includes
gates, doors and locks. Key control
of the locks becomes a problem
with large user populations and any
user turnover. Keys quickly become unmanageable,
often forcing the adoption
of electronic access control. Electronic
access control easily manages large user
populations, controlling for user lifecycle
times and dates and individual
For example a user’s access rights
could allow access from 7 a.m. to 7
p.m., Monday through Friday, and
expire in 90 days. Another form of access
control includes the use of policies,
processes and procedures to manage
ingress into the restricted area. The deployment
of security staff conducting
checks for authorized entry at predetermined
points of entry is usually supplemented
by mechanical and electronic
access control or simple devices such as
physical passes, ID and RFIDs.
The third layer is intrusion detection
systems or alarms. Intrusion detection
monitors for unauthorized access. It is
less a preventative measure and more
of a response trigger, yet it has a high
incidence of false alarms.
In many jurisdictions, law enforcement
will not respond to alarms from
intrusion detection systems. For example,
a motion sensor near a door could
trigger on either a person or a squirrel.
A simple sensor does not do identification,
and as far as it is designed, anything
moving near that door is unauthorized.
That is why CCTVs are the
next step in a layered security system
approach. Identification of the intrusion
event is essential for the required
Security cameras can be a deterrent in
many cases, but their real power comes
from incident verification and historical
analysis. For example, if alarms are being
generated and there is a camera in place, the camera could be viewed to verify the alarms. In instances when an attack
has already occurred and a camera is in place at the point of attack, the recorded
video can be reviewed.
Denying a breach
Guards have a role in all layers: in the first, as patrols and at checkpoints; in the
second, to administer electronic access control; in the third, to respond to alarms.
The response force must be able to arrive on site in less time than it is expected the
attacker will be required to breach the barriers.
In the fourth layer of perimeter security, a guard’s role is to monitor and analyze
video. Users obviously have a role also by questioning and reporting suspicious
people and aiding in identifying people as known versus unknown. Often,
photo ID badges are used and are frequently coupled to the electronic access control
system. Visitors are often required to wear a visitor badge.
Every application is unique, depending on the type of facility being protected,
its operating environment, its perimeter fence construction, its intrusion and security
history and the perception of threats.
Each individual site has a unique set of parameters that require a customized
perimeter solution. Just as the military cannot apply a one-solution strategy for all
military conflicts, neither can any perimeter apply a one-size-fits-all solution strategy.
Goals need to be established that are influenced by environmental concerns
(including any severe topography factors), the flow of traffic (foot and auto) and
the possibility of any major weather concerns. Effective PIDS account for all of
these elements and take budget into consideration. These factors weight the PID
system in varying degrees that impact its overall efficiency. Again, a layered system
is the best solution.
Once a PIDS solution is installed, the next critical step will involve a complete
calibration of the system. This calibration must account for all environments, sensitivity
and duration of any possible event breach. This ensures that any true positive
alarms will provide the best intelligence for the appropriate response. Thus a
proper PIDS solution provides the necessary forewarning for deterrence, delay,
detection and denying a breach.
Important design considerations derived from the aforementioned factors produce
a well-integrated PIDS. Design elements to be considered are:
Environmental design—Having intrusion detection sensors installed in the field
or on the fence.
Mechanical, electronic and procedural access control—Having an alarm processor
that drives and analyzes the raw sensor signals.
Intrusion detection, with appropriate response procedures—Having a security or
alarm management system that notifies security staff of an alarm and the location
of the intrusion.
Personnel identification—Having a communications infrastructure that ties
these three elements together and connects the system to the security staff,
along with an established and clearly documented site policy and alarm response
Militarily or commercially, whatever the perimeter’s greatest strength is, if left
ungaurded, it becomes its greatest weakness. Strengths and weaknesses of a security
system require a clear definition so policies and procedures can ensure appropriate
Intrusion detection technology will continue to advance, but
these advances will be focused more around software than hardware
as manufacturers continue to pursue improved system performance,
flexibility, and reliability.