Different Types of Walls and Security

by Alutrius Xavier


Fences are commonly used to protect the perimeter. The most common fence in use today is the cyclone fence, better known as the chain link fence. Fences are used as a deterrent and to prevent passage through the perimeter. Common ways of defeating fences are by cutting, climbing, and lifting. Cutting is not usually recommended for surreptitious entry, since it is easily noticeable. In this article, we will be taking the ‘Stealth’ approach. Climbing is most commonly done, but if the fence is in plain view, it may not be advisable since you can be seen easily. The higher the fence, the longer it takes to climb. The longer it takes to climb, the longer security has to detect and respond to your actions. Lifting is better since you are closer to the ground, and not as easily spotted, but the fence must be very flexible, or the sand very soft so you can get under the fence quickly and easily. Whenever you see a somewhat ‘unclimbable’ fence (or one that you just don’t want to climb) you should check the perimeter for large trees with uncut branches hanging over the fence or other objects which will enable you to bypass the fence without ever touching it. You could use a ladder but you don’t want to leave anything behind, especially with your fingerprints on it, not that you plan on doing anything illegal of course. Electric fences are not used for security purposes as much as they were in the past. Today, its main use if to keep cattle or other animals away from the perimeter (either from the inside or outside). There are devices which send a low voltage current through a fence and can detect a drop in the voltage when someone grabs onto the fence. Again, not too common. For high security installations, there may be 2 fences. An outer fence, and an inner fence which are 5-10 yards apart. It isn’t often that you see this type of setup, it is mainly used by government agencies and the military. You can be very sure that there are various intrusion detection devices mounted on the fence, buried underground between them, and/or line-of-sight microwave or photoelectric devices used. These will be mentioned later. If you insist on penetrating the perimeter, then you should try to measure how far it is between fences. Now find a 2 foot by X foot board where X is the distance between the 2 fences. Very slowly place the board on top of both fences. If there are no fence vibration sensors you can just climb the fence and step onto the board to walk across the top. If there are fence sensors, you will need a ladder which cannot touch the fence to get you on top of the board. You can then walk on the board, over the ground in between, and jump down, being careful not to disturb the fences. This will work if there are no sensors after the 2 fences. Identi- fying sensors will be mentioned later. Obviously the method of using a long board to put on top of the two fences will not work if the fences are spaced too far apart. Also, you and the board can be seen very easily.

Barbed Wire

There are two common types of barbed wire in use today. The more common and less secure is the type that is strung horizontally across the fence with three or more rows. The ‘barbs’ are spaced about 6″ apart, enough for you to put your hand in between while climbing over. Also, it is thin enough to be cut very easily. If you think you will need to leave in a hurry or plan on problem free surreptitious entry and the only way out will be to climb over the fence again you can cut the wire from one post to another, assuming the wire is tied or soldered to each post, and replace it with a plastic wire which looks like the wire you just cut. Tie it to each post, and come back anytime after that. You can then climb over it without being cut. The other type of wire, which is more secure or harmful, depending on how you look at it, is a rolled, circular wire commonly called Razor Ribbon. One manufacturer of this is the American Fence Co. which calls it ‘the mean stuff’. And it is. The barbs are as sharp as razors. Of course this can be cut, but you will need very long bolt cutters and once you cut it, jump as far back as you can to avoid the wire from springing into your face. As mentioned earlier, cutting is irreparable, and obvious. If the wire is loosely looped, there may be sufficient room in between to get through without getting stitches and losing lots of blood. If the wire is more tightly looped you may be able to cover the the wire with some tough material such as a leather sheet so you can climb over without getting hurt. This method is not easy to accomplish however. You may want to see if you can get under the fence or jump over rather than climb it.

Fence Mounted Noise or Vibration Sensors

Let’s assume you have found a way to get past the fence. Of course you have not tried this yet, since you should always plan before you act. OK, you have planned how you would theoretically get over or past the fence. You are now past the deterrent and prevention stages. Before you put the plan into action you had better check for the things mentioned earlier. If a fence is the first step in security defense, then fence mounted sensors are the second step. The types of detection equipment that can be mounted on the fence are:

Fence shock sensors: These mount on fence posts at intervals of 10 to 20 feet, or on every post. They are small boxes clamped about 2/3 up from ground level. There is a cable, either twisted pair or coax running horizontally across the fence connecting these boxes. The cable can be concealed in conduits or inside the fence itself, thus, making it hard to visually detect. Each fence sensor consists of a seismic shock sensor that detects climbing over, lifting up or cutting through the fence. So if the fence is climbable, it would not be wise to do so since you may be detected. Of course it doesn’t matter if your detected if there is no security force to respond and deter you. Another type, is called the E-Flex cable. It’s simply a coax cable running horizontally across the fence. This cable can not only be used on chain link fences, but can also be used on concrete block, brick, or other solid barriers. It may be on the outside, or mounted inside the fence, thus, making detection of the device harder. Of course detection of this and other similar devices which cannot be seen, doesn’t make it impossible. A way to detect this, is by simply repeatedly hitting the wall with a blunt object or by throwing rocks at it. If nothing out of the ordinary happens, then you can be reasonably sure it is not in place. This is basically a vibration sensor.

Low frequency microphones: This is essentially a coax cable that responds to noise transmitted within the fence itself.

Vibration sensors: These are based on mercury switches, a ring or ball on a pin, or a ball on a rail. Movement of the fence disturbs the switches and signals alarms. A hint that this is in use is that it can only be used on a securely constructed and tightly mounted fence, with no play or movement in it. Otherwise, they will be getting false alarms like crazy.

Now you know all about these types, how do you get around it? Well, don’t touch the fence. But if there is no alternative, and you must climb it, then climb the fence where it makes a 90 degree turn (the corner) or at the gate. Climb it very slowly and carefully, and you should be able to get over without being detected by these sensors! Make sure you climb on the largest pipe and don’t fall.

Security Lighting And CCTV

Sometimes, fences may be backed up by Closed Circuit TV (CCTV) systems to make visual monitoring of the perimeter easier and quicker. By installing an adequate lighting system and conventional CCTV cameras, or by using special low light sensitive cameras, the perimeter can be monitored from a central point. Security personnel can then be dispatched when an intruder is detected on the monitors. Some systems are stationary, and others can be moved to view different areas of the perimeter from within the central station. It would be in your best interest to determine if the camera is stationary or not. If so, you may be able to plan a path which will be out of the view range of the camera. If it is movable, you will have to take your chances. Light control sensor: This utilizes a Passive InfraRed (PIR) sensor to detect the body heat emitted from someone entering the detection area, and can activate a light or other alarm. PIR’s will be discussed in Part II of this series. The sensor has an option called: ‘night only mode’ in which a light will flash when a person enters the area, but only during night hours. It can tell if its dark by either a photoelectric sensor, or by a clock. Of course if its daylight savings time, the clock may not be totally accurate, which can be used to your advantage. If it is photoelectric, you can simply place a flashlight pointing directly into the sensor during daylight hours. When it gets dark, the photoelectric sensor will still ‘think’ its day since there is sufficient light, thus, not activating the unit to detect alarm conditions. This should enable you to move within the area at will.

Buried Seismic Sensors

Seismic detectors are designed to identify an intruder by picking up the sound of your footsteps or other noises related to passing through the protected area. These sensors have a range of about 20 feet and are buried underground and linked by a cable, which carries their signals to a processor. There, the signals are amplified and equalized to eliminate frequencies that are unrelated to intruder motion. The signals are converted to pulses that are compared with a standard signal threshold. Each pulse that crosses this threshold is tested on count and frequency. If it meets all the criteria for a footstep, an alarm is triggered. These sensors can even be installed under asphalt or concrete by cutting a trench through the hard surface. It is also immune to weather and can follow any type of terrain. The only restriction is that the area of detection must be free of any type of obstruction such as a tree or a bush.

Electronic Field Sensor

These detect an intruder by measuring a change in an electric field. The field sensors use a set of two cables, one with holes cut into the cable shielding to allow the electromagnetic field to ‘leak’ into the surrounding area. The other cable is a receiver to detect the field and any changes in it. Objects passing through the field distort it, triggering an alarm. This sensor can either be buried or free standing, and can follow any type of terrain. But its very sensitive to animals, birds, or wind blown debris, thus, if it is very windy out, and you know this is being used, you can get some paper and throw it so the wind takes it and sets off the alarm repeatedly. If it is done enough, they may temporarily turn it off, or ignore it due to excessive false alarms. It is not hard to tell if these devices are in use. You cannot see them, but you don’t have to. Simply get 3-4 medium sized stones. Throw them into the place where you think the protected area is. Repeat this several times. This works on the lesser advanced systems that have trouble distinguishing this type of seismic activity from human walking/running. If nothing happens, you can be reasonably sure this is not in use. Now that you can detect it, how do you defeat it? Well as far as the electronic field sensor is concerned, you should wait for a windy night and cause excessive false alarms and hope they will turn it off. As far as the seismic sensors, you can take it one step at a time, very softly, maybe one step every 30-60 seconds. These sensors have a threshold, say, two or more consecutive footsteps in a 30 second time interval will trigger the alarm. Simply take in one step at a time, slowly, and wait, then take another step, wait, until you reach your destination. These detectors work on the assumption that the intruder has no knowledge of the device, and will walk/run across the protected area normally, thus, causing considerable seismic vibrations. The problem with this method is that it will take you some time to pass through the protected area. This means there is more of a chance that you will be seen. If there are a lot of people going in and out of the facility, you may not want to use this method. Another way would be to run across the protected area, right next to the door, (assuming that is where the response team will come out) and drop a large cat or a dog there. When they come out, they will hopefully blame the alarm on the animal. The sensor shouldn’t really pick up a smaller animal, but odds are the security force are contract guards who wouldn’t know the capabilities of the device and the blame would fall on the animal and not you, assuming there were no cameras watching…

Microwave Systems

In an outdoor microwave system, a beam of microwave energy is sent from a transmitter to a receiver in a conical pattern. Unlike indoor microwave detectors, which detect an intruders’ movement in the microwave field, the outdoor system reacts to an intruders’ presence by detecting the decrease in energy in the beam. The beams can protect an area up to 1500 feet long and 40 feet wide. All transmission is line-of-sight and the area between transmitter and receiver should be kept clear of trees and other objects that can block the beam. Microwave systems can operate in bad weather, and won’t signal an alarm due to birds or flying debris. These systems work on the Doppler effect, in which they detect motion that changes the energy, and sets off an alarm. These devices will usually be placed inside a fence to avoid false alarms. These devices are very easy to visually detect. They are posts from 1-2 yards high, about 6 inches by 6 inches and there are 2 of them, one receiver and one transmitter. In some cases there will be more, which enables them to protect a larger area. To defeat this, you can enter the field, very slowly, taking one step at a time but each step should be like you are in slow motion. It doesn’t matter how hard you hit the ground, since it doesn’t detect seismic activity, only how fast you approach the field. If you take it very slowly you may be able to get past. Detectors of this type get more and more sensitive as you approach the posts. Ergo, choose a path which will lead you furthest away from the posts.

Photoelectric Systems

These systems rely on an invisible barrier created by beams of infrared light sent from a light source to a receiver. When the beam is interrupted, the alarm sounds. The beam can have an effective range of up to 500 feet. Multiple beams can be used to increase the effectiveness of the system, making it harder for you to climb over or crawl under the beams. Photoelectric systems can be prone to false alarms as a result of birds or wind-blown debris passing through the beam. The problem can be corrected by the installation of a circuit that requires the beam to be broken for a specified amount of time before an alarm is sounded. Weather conditions like heavy fog, can also interrupt the beam and cause an alarm. This can also be corrected by a circuit that reacts to gradual signal loss. These systems should not face directly into the rising or setting sun since this also cuts off the signal beam. As you can see this system has many problems which you can take advantage of to bypass this system. As with any system and method, surveillance of the facility should be accomplished in various weather conditions to help verify the existence of a particular detection device, and to see how they react to false alarms. Many times, you will be able to take advantage of various conditions to accomplish your mission. If there is only one set of devices (transmitter and receiver), try to estimate the distance of the sensors from the ground. You can then either crawl under or jump over the beam. This also works on the assumption that the intruder will not recognize that the device is in use.


Guards: There are two types, in-house or company paid guards and contract guards. Contract guards are less secure since they do not work for the facility and if they make a mistake they simply get transferred to another facility no big deal. In-house guards know the facility better and have more to lose, thus, they are probably more security conscious. Be aware of any paths around the perimeter in which guards can/will walk/ride to visually inspect the exterior of the facility.

Central monitoring: Monitoring of the devices mentioned in this article is usually accomplished at a ‘Central Station’ within the facility. Usually, guards *SHOULD* be monitoring these. If you have planned well enough, you may find that the guard leaves his/her post to do various things at the same time every night. This would be an ideal time to do anything that may be seen by cameras. Unfortunately, there will probably be more than one guard making this nearly impossible.

Gates: Probably the easiest way to pass through the perimeter is to go through the gate. Whether in a car, or by walking. This may not be too easy if it is guarded, or if there is a card reading device used for entry. Exterior card readers: For now, if the card used is magnetic (not Weigand) it is quite possible to attack this. If you have an ATM card, Visa, or other magnetic card, slide the card thru, jiggle & wiggle it, etc. and quite possibly the gate will open. Reasons for this are that since it is outside, the reader is subjected to extreme weather conditions day in and day out, thus, the detecting heads may not be in the best of shape, or since it is outside it may be a cheap reader. In either case, it may not work as good as it should and can make ‘mistakes’ to allow you access.

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