Elements of a Security System – Part 2, by J.M.

(Continued from Part 1.)

The final aspects you need to consider when planning a security system are the types of threats you need to be able to detect. If you live in a wooded area where there are a lot of experienced woodsmen and hunters, you’ll have to consider how to detect people that know how to move silently and effectively and are more likely to notice things like tripwires or trail cameras. On the other hand, if you’re in an area that may primarily experience urban sheeple migrating in search of resources after a disaster, your security situation will be simplified, since most of those folks will take the path of least resistance with minimal regard for stealth. An absolute worst-case scenario would be trying to set up a security system to detect people that have military training and equipment, since they will tend to be more observant about wires, alarms, infrared light, etc. As with any system, the more complex and extensive you make it, the harder it will be to maintain and the more likely you are to get a lot of false alarms.

Once you understand the primary drivers for your security system, you should begin to develop an overall approach to how you want to implement it. The best approach is to leverage what the military refers to as ‘defense in depth’ – layers of detection capabilities at different distances from your house or property. The goal is to have multiple opportunities to detect an intruder in case they get by one of the perimeters. Remember that to stay safe in a fixed location you need to be able to detect every intruder approaching from any possible direction at any time, but an intruder only has to be lucky or good enough to get through your detection perimeter once to do some harm.

Reducing Your Attack Surface

In the cybersecurity industry there’s a concept known as an ‘attack surface’, which is the sum of all of the possible ways a computer can be attacked. To minimize the resources required to monitor all possible paths, one common recommendation is to block off as many attack vectors as possible so they can’t be used. This concept can also be applied to designing a physical detection system by minimizing the number of possible ways an intruder can approach and move through your property, thereby reducing the number of paths you need to monitor.

There are a lot of options for accomplishing this, such as adding obstacles or landscaping. For example, a high fence that completely surrounds your property would force an intruder to either approach through a single gate or attempt to scale the fence, where they can be more easily detected and dealt with. However, for many of us this is not an option, so you should focus on limiting possible approaches as much as possible. Even if you can’t fully enclose your property with fencing you may be able to install some stretches to funnel an intruder down certain paths, making them easier to detect. Rolls of concertina (razor) wire can also be used, or thorny bushes such as Honey Locust, Blackberry/Raspberry, Roses, Bougainvilleas and Pyracantha can be planted. You can even pile up bunches of loose branches and other debris, which most people will naturally go around. If you live near a stream or other body of water you may be able to divert some water to low-lying areas and turn them into mud pits, which most people will avoid.

If you’re trying to protect a building you should also consider radial obstacles – these are fencing, concertina wire, thorn bushes, etc. that start at the building and move straight out. If you have a house where an attacker could get close and move around the house unseen below the window level, radial obstacles would force them to move away from the building and potentially expose them to observation and detection.

When planning obstacles to funnel intruders you should attempt to reduce the potential for those obstacles to provide the intruders with cover and concealment. While a solid-wood fence may force an attacker to move down a different path, it is also something they can potentially hide behind, so chain-link fencing might be a better option. When planning obstacles to funnel intruders, draw them out on a map and simulate them with full-sized wood or cardboard mock-ups to see how they impact your view of the approaches. If you’re forced to deal with obstacles that provide cover or concealment, you may need to plan on some additional capabilities that can improve your ability to detect and observe an intruder hiding behind those obstacles (more on that later).

General Design

Once you’ve defined your requirements and general approach, your next consideration should be what types of sensors and alerting you want to implement. Note that for the purposes of this article I’m not covering direct visual observation as a detection method, although it can be utilized as one in combination with the other types of sensors if you have the personnel available to keep watch. Activities such as active patrolling can also extend your awareness of your surroundings, but it requires qualified people.

The sensor (or trigger) is the component that actually detects the presence of a person or vehicle and triggers an alert, and comes in two general varieties:

  • Direct contact – A person/vehicle directly interacts with the sensor, or something the sensors is connected to, to trigger an alert. These include tripwires, pressure mats, door opening sensors, etc.
  • Proximity – The nearby presence of a person or vehicle causes the sensor to trigger an alert. These include motion detectors and magnetic vehicle sensors.

Direct contact sensors generally have the advantage of fewer false alerts, but they can only usually provide coverage for a relatively small area or limited range of intruder actions. Proximity sensors let you cover a broader area, but tend to be more prone to false alarms from animals, moving branches, blowing snow, etc. You can and should leverage both types of sensors, using each where it makes the most sense for your requirements. Consider a situation where you want to alert on someone entering a room that has several doors and windows – you could install one motion sensor to cover the doors and windows, which may be subject to false alarms from your dogs or sunlight, or you could wire sensors directly to each door and window.

Alerting is how your security sensors interact with humans and notify you when something happens, so you also need to consider how you want to be alerted if a sensor is triggered. There are two possible implementations to consider:

  • Centralized/Remote – The remote sensors send an alert signal to one central location, like a security station.
  • Local – Alerting occurs where the sensor is triggered.

A centralized system has the advantage of collecting your alerts in one location and can provide you with better spatial awareness of which sensor was triggered, but it can be more complex to implement since you’ll need some method to send the sensor signal to that central location (either wires or wirelessly). You’ll also need to have a person at or near the centralized alerting location to monitor for alerts, or have audible alarms loud enough to wake you up. Another significant advantage of centralized alerting is that since the audio or visual alarm doesn’t happen near the sensor, an intruder may not realize they’ve been detected, which could give you more time to intercept them and take action.

Local alerting means some form of sound or visual signal is generated at or near the sensor’s location, such as a tripwire ringing a bell, so it’s a lot easier to implement. One down side of local alerting is that with sound-based alerts (e.g. blanks, siren, bells, etc.) it may be difficult to localize exactly where the alert is coming from; another disadvantage is that the intruder will know they’ve been detected and may take rash action. Local visual alerts such as flares or smoke bombs also require that someone see them to be effective, and some of them may not be as visible at night or in heavy weather conditions such as rain or snow. One possible approach would be to combine audible and visual alert signals for local alert sensors so they are more likely to be noticed and localized across a wide range of conditions.

As with sensors, you can apply a combination of both centralized and local alerting to meet your requirements. For example, you could have sensors at distant strategic locations that that uses aerial flares combined with audio alarms to alert you that an intruder has entered your area, which would allow someone to get to the centralized alert console to track their progress and radio directions to a response team.

For my personal system I’ve planned and (partially) implemented a four-layered sensor approach – the more distant remote sensors at strategic locations will use local alerting with 12GA shotgun blanks and flares, and the outer, inner and interior perimeter sensors all feed back to a central console in my house with a mix of wired and wireless signals. Note that I’ve planned, designed and built the remote strategic blank/flare sensors, but I won’t install them until things really go pear-shaped. I’ve drawn a map of my house and property on a piece of ¼” plywood and installed 12V automotive panel lights/buzzers that light up and buzz when the corresponding sensor is triggered. Here’s an example of what the board could look like (NOT my actual property layout!):

I’ve run the wires to the wired sensor’s locations over the course of normal yard and house work. The sensors are a combination of tripwires, motion sensors and Reed switches that cover obvious trails in the woods, the area right around my house and doors and windows in my house. When any sensor is tripped, it closes the 12V circuit and triggers the corresponding light/buzzer on the console. I’ve also installed some switches on the console that allow me to disable any of the alert zones if necessary. The system is not that complicated, and only requires a basic knowledge of how to wire a light/buzzer and a switch to a 12V power supply.

(To be continued tomorrow, in Part 3.)


  1. Deny, disrupt and channelize. An attack can happen swiftly, and set off all intrusion devices, and overwhelm. Even with a well maintained perimeter, they could chose a point and punch hole, and ‘hey dittle, dittle, right up the middle’, here they come. It would be better to given them a ‘convenient’ entry point, and funnel them up into a choke point that can make it easier for defenders take them on, one by one, than to attempt to defend flanks, let alone the perimeter. Alarms can have your ‘6’, and obvious wires or other obstacles, can make attackers more selective as they will access your defenses before hand. Block ingress with fallen tree, use cross fencing, or sections of c-wire, deny the micro terrain, dead zones, and cover with barb wire, stakes in the ground, and so on, to shape the battlefield, and prepare it to work for you. They will predictably take the path of least resistance, and travel in straight lines unless channelized… like rats in a maze, into the funnel and then the choke point.

  2. Again, an excellent article submitted by this contributor (The one on patrolling was awesome).

    For when things do go “pear shaped” and conditions allow you to go into maiming/lethal mode with your devices, a good prep to have is military surplus MINE markers. These are the classic upside-down facing triangular red NATO signs made out of sheet metal, with holes punched into the top corners for running 550 cord, commo wire, string, etc. through them.

    Hang these lines with signs attached at, or just below eye-level (for children, or any other people within your perimeter) on YOUR side of the area planted. Even if you have to mark more than one side due to gardens, walkways, etc., it’s better for the bad guys to see those same markers, rather than take the chance of a loved one tripping the devices.

    And last but by no means least, chart where every device is planted. If you’re an intell/operations veteran and like to do Situational Templates (SITTEMPS), booby traps have their own by-the-book symbology, along with various types of obstacles, mines, etc.

  3. Random thoughts: When I built a fence it was a “semi-privacy” fence – standard pressure treated 1″X6″X6′ dogeared pickets, cut to 5’6″; yes, someone can look over to see in, but I can easily look over to see out and seeing threats 200 meters away is more valuable. Pickets were spaced 1″ apart, which saved 18% on picket costs and made anyone moving outside the fence visible through the gaps while still providing quite a bit of privacy (yes, it’s possible for an intruder to peek through the gaps but that’s less of an issue than an intruder being able to hide unseen outside the fence). A wedge-shaped section of scrap 4X6 (I used 4X6 posts instead of 4X4) lag bolted 12″ above grade to the face of every 2nd fence post serves as a small step and a 3/8″ lag bolt inserted into the side of that post 5′ up at a 30 degree upward angle to serve as a stability handle to assist shorter people standing on the 4X6 wedge “step” so they can see over the fence (drill the post, screw the lag bolt in, cut off the hex head; the upward angle prevents using it for a rope anchor, removing the hex head means anything tied to it and pulled upward will slide off). Tip: a tall privacy fence – approx 6′ high – will require 3 horizontal supports between posts to support the pickets. The top and bottom horizontals can be 2X4s, but make the middle horizontal at least a 2X6, use a 2X8 if you can budget for it. The fence pickets will absorb rain and get heavy, if it rains a lot they’ll stay heavy (places like Florida they won’t dry out for the entire summer) and the fence will sag. A heavier-than-standard center horizontal will prevent that.

    Security fences need to be screwed together, including the picket-to-horizontal connection. Nails and staples eventually work out, staples especially can be pulled out by pulling on the pickets. Stainless flat head screws are the way to go. More expensive, but you’re buying them only once, they can be salvaged if you take the fence down, and whatever you spend on high quality materials is much cheaper than the labor to rebuild the fence in several years.

    Like the article’s author, I needed to run wiring from “home base” to positions on the perimeter. I bought a used electric chain saw with a 12″ bar and used it as a trenching tool. Tip: Make brackets to hold the saw and clamp/bolt the brackets to something with wheels; I used a hand truck. It makes it much easier to use for trenching and helps keep the trench straighter. Yes, it will ruin the saw, but I got about 1,000 feet of 12-inch deep trench out of my $20. Tip: When putting electrical wire/cable into the trench, pressing it in with a “pusher tool” of 1/4 plywood works well – a 12″ width that’s rounded on the corners works. Tip: Put multiple cable runs in, one at a time, so you have spares already in place. Waterproof the ends of the spare runs. Cable is cheap, trenches are expensive. As the author stresses, DOCUMENT THE LOCATIONS OF THE RUNS. Make a map, use a compass and measuring tape. (Which is also useful for everything else – water lines, sewer/septic lines, septic tanks, buried electric/phone/internet, TV cables, etc. ALWAYS CALL THE LOCAL BURIED UTILITY LOCATING SERVICE BEFORE DIGGING/TRENCHING. If you wind up cutting your neighbor’s (or even your own…) TV cable, phone or well line you’re fully liable for the cost of repair/replacement – which is NOT cheap. If the locating service mis-marked it you’re off the hook. If you’re doing any serious digging work, it pays to put in sprinkler pipe as underground conduit at the same time. Sprinkler pipe is thin wall, lighter than schedule 40 and considerably cheaper. It comes in 10 ft lengths from home centers but can be had in 20 ft lengths at irrigation supply houses (fewer connection unions saves money). Use 3/4″ even though 1/2″ is cheaper because 3/4″ is easier to pull wire through, and if you’ve got the budget for it, 1″ is much better. Buy a roll of “pull string” – synthetic heavy string used for pulling wire through conduit – and put it in the buried pipe when you bury it. Always add a length of pull string to whatever cable/wire you’re pulling through the pipe so there’s always a full length of pull string in the pipe for future use. FYI, thin wall irrigation pipe does NOT meet electrical code requirements for buried conduit so if you’re installing high voltage runs (120 volt, 240 volt) you’ll need to use the gray (schedule 80) plastic conduit. Tip: Whatever you’re doing, it’s a big plus to use at least one size up from what you think you need; heavy plastic code-compliant conduit, whatever it costs, is much, much cheaper than the trench it’s going into.

  4. I hesitate to offer this idea, given the relatively sophisticated alternatives mentioned, but for someone who is trying to increase their security situation in a urban/suburban setting or who is located in an area with relatively few avenues of approach or easy access, there is one inexpensive alternative that could greatly increase a defense profile.

    Harbor Freight makes a wireless driveway alarm: https://www.harborfreight.com/search?q=wireless%20driveway%20alarm. While it is regularly $24.95, I see it on sale a few times a year for $9.00. (Everything at Harbor Freight is on sale very often!) The description says that it has a 400 foot range that will signal the approach of a vehicle or a person.

    I took it to my bugout location. I asked a friend to help me test it. Given how frequently ranges for FRS radios are grossly exaggerated by manufacturers, I wanted to see just how good this little device would actually perform. It turned out that he had already tested the one I gave him. It had successfully sent a signal at least 300 feet through rough brush. I thought, “Not bad at all.” And for $9.00?

    The product description says that it is weather-proof. Of course, a coat of paint would be appropriate, preferably a color that blends with its background.

    I have no information concerning its durability. I placed the unit across the sidewalk leading to my front door. Because I was running in and out of the house so often, the unit drove my wife nuts and I removed it. Happy wife, happy life.

    Wait for it to be on sale and then buy one for $9.00. If it works well in your setting, perhaps additional units placed in an interlocking setting around your property perimeter would be a nice addition.

    1. I second your recommendation. I’ve had one of those units in my driveway for 10 years+. It is excellent. Few false alarms and ridiculously cheap! Plus our dog-before she went deaf-learned what it meant and would fly up onto the back of the couch barking like mad which helped me determine by her bark if it was a cat, deer or person coming up the way!

      1. Spotlight,

        I made a mistake. The regular price for the unit is $14.99, not $24.95, so even when it is not on sale, it is modestly priced.

        That you got over 10 years of use from it is good news.

  5. Survivorman99,

    Dakota Alert makes two different MURS alert systems – one uses motion detection, like the Harbor Freight one you mentioned, and one uses a magnetic sensor to detect large chunks of ferrous metal, like cars. The motion one is always going to be a lot more sensitive to false alerts, since pretty much any motion can set it off. The magnetic one will generally only alert on vehicles. Both definitely have their uses, it just depends on your requirements. The HF one you indicated is definitely a lot cheaper for a motion sensor option, which would allow you to deploy more of them and have some spares, but it requires a dedicated base station, whereas the Dakota ones will broadcast on a MURS radio frequency. Again, which one makes the most sense depends on your needs. FYI – I have another article coming up sometime in the future on how you can integrate a radio broadcast into you security system.

  6. Yes, driveway alarms like the Harbor Freight model do require a dedicated base station, although that base station would consist of perhaps multiple receivers within earshot of the homeowner. I’m thinking that someone who has been hunkered down for days inside a home in the suburbs would benefit from models like this that began to chime at night because a two-legged predator entered the backyard. The base station(s) on a nightstand next to the bed could be critical in providing an extra minute or two to react, locate, and engage the threat–and each of them at a cost of not much more than a Big Mac Combo meal, or a 6-Pack of Boston Lager.

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