Comparison Underground Perimeter Intrusion Detection System Tech

Comparison Underground Perimeter Intrusion Detection System Tech

In the last couple of years, the use of buried sensor for perimeter intrusion detection system, becomes very popular due to the advantage of been a discreet or even an invisible detection system and avoiding the need to build an above-the-ground fence to protect the perimeter due to costs or environmental reasons.


Buried Perimeter Intrusion Detection Systems are used to protect (among others)


  • Borders
  • Oil & gas pipelines and facilities
  • Military bases and other land facilities
  • Airports and seaports
  • Prisons
  • Farms
  • Airports


Underground Intrusion Detection Systems Advantages


  • Invisible system, the intruders can’t see the underground intrusion detection system
  • No need to build anything above ground level
  • No need for line of sight as required by some security products such as radars, Microwave, IR and video systems.
  • Quick and easy installation (in some cases especially SensoGuard’s Invisifence)
  • Easy maintenance (in some cases especially SensoGuard’s Invisifence )


Three types of Buried Perimeter Intrusion Detection Systems


There are several systems based on different technologies for creating buried intrusion detection system.


  • Seismic sensors system– seismic sensors are buried underground and by recognizing vibrations in ground, they detect and locate intrusions. In this article we focused on invisiFence by SensoGuard as the ultimate seismic sensors system.
  • Leaky coax system –the buried leaky coax cable creates an electromagnetic volumetric detection field. The controllers monitor this field to detect and locate variation caused by intrusion.
  • Fiber Optic system– central controller transmits pulses of signal and analyzes the reflections and disturbances to detect and locate intrusions.


We will focus on the following subjects when comparing the three: performance, installation requirements, limitations and costs.


Systems Topology Description


  • SensoGuard Seismic Buried Perimeter System (InvisiFence) composed of seismic sensors strings connected to a local processing unit every 50m and a central hub unit every 1000m.
  • Fiber optic systems- composed of a central controller which can analyze a very long fiber optic cable (up to 80km).
  • Leaky coax system- composed of leaky coax cables connected to a local controller every 400m (for single cable).


Buried Perimeter Intrusion Detection Systems Installation Considerations and Limitations


All buried systems require digging a trench for placing sensors/cable. However, limitations regarding installation environment and installation depth are different from one system to another.


  1. Seismic Buried Perimeter System (SensoGuard’s InvisiFence)
    The trench depth is 30-50cm (precise depth is not an issue, can be anywhere between 30cm and 3m)
  2. Fiber Optic system
    Installation depth accuracy is a critical (no more than 20cm)
    If installed deeper (30cm for example) the system performance will be greatly reduced.
    Shallow installation increases the possibility that cable will be exposed over time (due to environmental elements such as wind) or the detection performance will be poorer overtime if additional soil or vegetation will be added or grown above ca
  3. Leaky Coax cable
    • Installation depth accuracy is critical. The system’s performance will be compromised if the cable is placed deeper than recommended (23cm for example). Shallow installation increases the possibility that cable will be exposed over time.
    • System cannot be placed near metal objects – such as metal fences or metal pipes.
    • Water / snow above the system will cause false alarms. The RF signal cannot bypass water/snow, resulting in poor system performance and false alarms in case of puddles or snow on the ground.


Maintenance after Installation


Among the 3 technologies, the fiber optic system is the most complex system to repair in case of fault. Fiber optic cable replacement is a very sensitive process and there is always the chance of additional mechanical damage during the repair.

Leaky coax systems are easier to repair than optic fiber systems but harder to repair compared to SensoGuard’s InvisiFence. Not always easy to find the faulty point and required to keep the installation requirement and drainage.

All of SensoGuard invisiFence components are replaceable easily and quickly.

Leaky coax systems require periodical calibration due to changing condition of soil above the system. The changing conditions will affect the system sensitivity and false alarm rate. In contrast, SensoGuard buried perimeter system doesn’t require periodic calibration after installation.


System Costs


For projects of several km – SensoGuard buried perimeter system and leaky coax are cheaper than fiber optic system.

For projects above dozens of km – fiber optic system is the cheapest option.

InvisiFence is cheaper for projects of less than 2km.


Performance & False Alarms


All three perimeter security systems: SensoGaurd’s Invisifence, the leaky coax system and fiber optic cable system are buried systems that detect above the ground movement. However, Invisifence does stand out as the most reliable one for three reasons. The first, the actual depth of Invisifence can be anywhere between 30cm-3m without any decrease in the system’s performance. That means that you can bury the system deeper or in case soil will be added (in desert, or after a storm), the system will continue to function without any problems.

In contrast, Leaky coax and fiber optics systems are very much affected by depth. If you bury them too close to the ground or deeper than advised, their performance will be greatly compromised. Secondly, InvisiFence is less affected by environmental changes. While Leaky Coax and fiber optic systems may set off false alarms in case of puddles or growing vegetation, InvisiFence seismic system will by far more reliable and will not set off false alarms in such cases.

Lastly, InvisiFence has smart adaptive deep-learning algorithm. By using the algorithm, the system constantly learns and adjusts to its environment. The system constantly sets a new signature of what is the “normal” state of things in order to detect intrusions and avoid false alarms. Based on environmental changes such as new road or vegetation, the normal state signature is always revised. InvisiFence is the only system which makes the needed adjustments to detect threats without the need of making any external changes.



Perimeter Intrusion Detection: Comparison between 3 Systems Seismic, Fiber Optic and Leaky Coax





Summary: Which Underground Perimeter Intrusion Detection System is preferred?


In one sentence, SensoGuard seismic InvisiFence Plus system is the best choice of the three technologies.

Let’s look at it with more details. Fiber optic systems are more expansive and less reliable than Leaky Coax or seismic systems. So the choice is really between Leaky Coax systems and InvisiFence Plus seismic system.

InvisiFence Plus is far more reliable in terms of threat detection and avoiding false alarms. It is also easier to install which makes it superior to Leaky Coax systems.

As for costs, for securing perimeter of several km, InvisiFence Plus is cheaper than both Leaky Coax systems and fiber optic systems. However, in perimeters of above 10km, Fiber optics systems are cheaper.

SensoGuard’s  InvisiFence Plus is the best cost effective underground perimeter intrusion detection system in the market today.


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