Prepping 101: Perimeter Alarms – Low Tech Security for $20

The contraption in the middle is the sentry alarm. As you can see, it is a DIY welded project, available on Ebay for $20 plus shipping.

The contraption in the middle is the sentry alarm. As you can see, it is a DIY welded project, available on Ebay for $20 plus shipping.


On Ebay: Sentry Alarm Mines

I have pondered the subject of perimeter security for some time and I have decided that it is probably the hardest to come up with a hard and fast rule. You have to sleep at some point. And even if you have enough people to keep watch, how much advance notice will you have? I have looked into 12 volt motion detectors, but so far I have not found a better option than these hand welded alarms on Ebay. They use a standard .22 short nailgun blank, available at Home Depot. If you are handy you could make them yourself, but at $20 each they are a pretty cheap investment for a pretty important aspect of long term survival.

Officially these “alarm mines” are made for paintball games to simulate a military Claymore mine. I purchased mine several months ago and it didn’t come with any paperwork, but apparently there are now directions and warning signs. Please check the legality of them in your local jurisdiction, but for the most part, they are harmless and not considered a “booby trap,” which are of course totally illegal. It also goes without saying to avoid doing stupid things with them, like setting off other charges and whatnot.

The mine works by releasing a spring captured nail. It hits a .22 caliber nailgun blank, creating a report.  That ring on the end is tied to the trip wire, and you can see the blank holder at the bottom. This will not hold a live .22 caliber round with a projectile. There is a small space at the bottom to exhaust the gas from the blank.

The mine works by releasing a spring captured nail. It hits a .22 caliber nailgun blank, creating a report. That ring on the end is tied to the trip wire, and you can see the blank holder at the bottom. This will not hold a live .22 caliber round with a projectile. There is a small space at the bottom to exhaust the gas from the blank.


If you look at the pictures, it is easy to understand how the alarms work. The housing has both stakes to mount the alarm in the ground, and holes to mount the alarm on a tree or post. The trigger is just a spring captured nail that you raise and rest on a flat bar. Tie the trigger ring to some monofiliment, and you have a trip wire. When the monofiliment is walked into, or tied to a trigger object (see below), the trigger is pulled off the bar, mashing the .22 rimfire blank and setting it off. The simplicity of the design is genius, and best yet, it works. I tried it with 6 lb. monofiliment both stuck in the ground and mounted to trees. You wouldn’t think that those little legs would be strong enough to hold the unit in the ground as you walk by the trip line but the tines are set up perpendicular to the trigger so even in soft Florida sand they work great.

You will find the .22 rimfire blanks at Home Depot, Lowes, or even on Amazon. These are not the flat blanks for starter pistols, though those would work as well. The nailgun blanks are much more powerful and much louder. They come in level 2 to level 5, but I have only seen them for sale up to level 4. In backyard testing, the level 4 are not twice as loud as the level 2, but they are definitely louder. They are also harder to remove from the alarm, but not so hard as to be prohibitive.

The blanks are available at home supply and online for about 3 cents each. I suggest the level 4 which are the loudest I could find.

The blanks are available at home supply and online for about 3 cents each. I suggest the level 4 which are the loudest I could find.


No mater how many of these alarms you put out, in a real survival situation you will probably only get one good warning shot. Once you know what to look for the alarms are easy to spot, even with very thin monofiliment. That most attacks will come at night is a plus with these, because you may get more than one trip, but no attack is a good attack.

If you have a bugout location already picked out, your most valuable resource in to think like trapper. If you have never looked into this hobby and profession, the trap is never about where you think the animal might walk. Successful trappers learn the art of guiding the animal into the trap. You do this by creating a path of easy travel surrounded by paths of difficult travel, without it looking like the situation was created for the trap.

In my example here in the pictures you can see that I mounted the alarm horizontally on a tree, so the trigger is a downward motion. Then I found a path between a tree and brush pile that I can encourage a human predator to take by laying brush and trees without a dozen yards or so on both sides.

The tines on the bottom of the alarm are set perpendicular to the trigger, so even in soft soil they work great.

The tines on the bottom of the alarm are set perpendicular to the trigger, so even in soft soil they work great.


So the route doesn’t look like a door, and the perfect place for a booby trap or ambush, I lay a stick across the path as if it fell there. This gives the illusion of nature, while still retaining the path of least resistance, which like electricity, bad guys always seem to seek.

When the bad guy kicks the stick out of the way, or steps on it, the alarm will sound. He may light up with a gun, firing into the woods, but he doesn’t know that he just alerted the sentry 1/4 of a mile down the path, and one that will never be hit by his wasted bullets.

Sounds pretty tactical and romantic huh? Just remember that real life is what happens when you are making other plans. These alarms are about as scary a survival item as you will purchase, because if they work as promised, you have a threat on your doorstep, and who knows how big a threat it will be. The very best any of us can hope for is to gain an awareness advantage, and if need be, bug out of the bug out. These alarms may give you an edge at best if a gunfight is inevitable, and because they are so low tech, there is little chance that they will fail.

This is a set that will work far better than a strip line that can be easily seen and stepped over in daylight. The unwelcome visitor is funneled between a brush pile and a tree, that has been blocked by an easily moved object. The object is attached to the trip wire so when it is stepped on or kicked aside, the alarm will sound.

This is a set that will work far better than a strip line that can be easily seen and stepped over in daylight. The unwelcome visitor is funneled between a brush pile and a tree, that has been blocked by an easily moved object. The object is attached to the trip wire so when it is stepped on or kicked aside, the alarm will sound.


Please note also that this Ebay seller was not given a proper heads up about the sales coming in, so he may be a bit overwhelmed. If you are one of the early readers on Monday morning you might want to get int there and get yours before the late readers click in. I will at least email him that he may see some orders this week.

This is where the holes on the side of the alarm come in handy. For this set it is mounted horizontally so that the trigger pulls down. I tried this and it tripped every time.

This is where the holes on the side of the alarm come in handy. For this set it is mounted horizontally so that the trigger pulls down. I tried this and it tripped every time.

{ 11 comments… add one }
  • MichaelAngel October 31, 2017, 6:48 pm

    As you are setting your Devices Spread around a Few old Kites…..Like some Kids were playing……Make Sure there is Plenty of String laied around ……Then your Trip Wires ……False sence of Security

  • Miles Hokum February 19, 2015, 6:22 pm

    The Guns America purchases wiped out my inventory but THEY’RE BACK! Please visit http://www.alarmmine.com

  • Mason Hamilton October 27, 2014, 1:51 pm

    Way over thought (typical gadget addiction presentation) and unnecessarily expensive. You can accomplish similar results with a mouse trap and a cap-pistol cap (or several) taped under the mouse traps spring loaded bar. Caps can also be used to set-off secondary fireworks to make the alarm louder.

    Additionally, the trap’s base board can be drilled for a CF shell primer, black powder primer, or .22 nail gun propellants. A firing pin can be created with a tack soldered to the trap bar properly aligned with the primer objective. If you want to use more than once – then you can case the primer or .22 with a piece of tubing drilled and epoxied into the wood. A washer, wood or metal plate can be used to cover the primer as a safety while setting the “alarm” and until ready to activate.

    Setting the “alarm” in horizontal container (bucket, pipe, etc.) that doesn’t interfere with the “alarms” activation or action – can focus the sound on your base location to make it more audible to you and not your surroundings, rather than have the sound spread 360 to surroundings and diffuse it’s audible strength. Container additionally helps weather proof “alarm.” The added benefit is you can a little peanut butter-on-twine to the trap and catch a few rats as well – when the system is not in the “alarm” mode. Any prepper list should include a few dozen rat traps – for lots of creative uses.

    • Russ October 27, 2014, 3:03 pm

      I like the ideas. Thanks Mason

      • Mason Hamilton October 28, 2014, 12:17 pm

        The humble spring loaded rat trap has the necessary stored energy to accomplish quite a few initiation/ignition tasks – from alarms to even defense devices – in a survival situation. They are very trigger sensitive and adequate safety additions are essential. Additionally beside ridding the camp of damaging pests, they can also be used (if baited properly to trap squirrels, other small mammals and we’ve even caught birds in them).

        I’ve always wanted to add some soldered needle like “teeth” to the bar facing downward going into drilled receiving holes in the base plate and a row of teeth (small nails?) facing upward from the base beneath – inter-meshing with the bar “teeth” and see if would catch a fish. Because of the wire bars low profile/lack of resistance in the water and resulting speed and force in closing, it might work. Definitely have to secure the trap on a line. Worth a try when we have time. Given their price, size and wt. they’re hard to beat as a creative survival resource – use your imagination.

    • Mahatma Muhjesbude December 15, 2014, 1:14 pm

      Yeah, Mason, you must live in Wisconsin where there’s ‘NO FREAKING TRESPASSING ALLOWED!’ PERIOD! LOL!

      Obviously I’m not going to advertise some really ‘pro-grade’ apocalyptic perimeter defenses even though the ‘know how’ is out there and you can find it but i don’t want to make it too easy for amateur bubbas to hurt themselves or handfeed dangerous idiots with easy info. But the intrepid reasonable survivalist should definitely explore the possibilities and put two and two together and you can come up with serious ‘combat’ type devices that will really do the job in a world gone mad if you really need them when the time comes.

      I like Rat Traps also for a lot of reasons. I’m talking about the heaviest duty ones–not the small mouse traps. You can easily ‘modify’ these by either cutting the business end of the wire and bending it to where it comes down like a spike after sharpening or fastening a sharp nail on it. If somebody steps on it with their shoe they will definitely recoil in fear and probably pain as it stays on the shoe when it ‘grabs your foot’. It’s bad enough if you are wearing a soft shoe even stock without any modifications! But a ‘spiked’ modification will penetrate boot leather. Put a bunch of these on a trail in a three step radius, And these are not illegal because you are just trying to catch those nasty ass GMO’s Franken Rats invading your entire property.

      Along these lines, serioius larger animal spring traps work even better if you get one that will capture most of the foot when stepped on. You can also stake them in the ground on their chain or tether them to even small trees and they’ll also have an ‘audible’ alarm as the intruder starts screaming from the pain and can’t get away easily and is…literally…’trapped’.

      Technically these are not illegal ‘dangerous boobytraps’ as you can say all day that you are just trying to catch that nasty 4 legged coyote or bobcat that’s sneaking around your house trying to eat your chickens or other pets, or bite you? So you
      were lucky they were there when the two legged predator came sneaking around! Just make sure you have a ‘trapping license’ if those are required in your state.

      I personally like the fireworks loud retorts in a perimeter set up. If you do them right and put them high enough in a tree so they can’t otherwise hurt anyone because some of these which you can get legally can also replicate a flash /bang, the concussion and surprise of some of the larger legal ones like the mortar shells or some rockets with a full legal oz. of flash powder in them, (remove the charge from the rocket, and set it up to explode on a trip) will skeeer the BeJEEsus out of a malicious intruder when it cracks above their heads like the ‘thunder of God’, and if it’s at night, it might also temporarily kill his night vision and hopefully he’ll stumble into a tree or step into one of your other devices, knock himself out, and you can tie him up and ‘water board’ him a little for fun before the deputies come and take him away to jail.

      And remember, it’s no fun preventing intrusion if you cripple your own family or animals, or you ‘anti-intrusion’ yourself because you forgot about them. Make sure you know what you are doing.
      If you’ve had no real experience with chemicals and fuzes and fireworks, though, it’s best to just use mechanical anti-intrusion preventions. I know a person who doesn’t like to play with fireworks because his brother lost a finger with them, but he bought several of those orange colored plastic marine flare guns from Walmart, which are to me a little too expensive, but he tapes them to a tree and spray paints them camo and ties a wire to the trigger for the trip and replicates a real military style trip flare that can be re-used and re-set over and over with different kinds of flares and retorts and even pepper spray rounds. By the way, if you have the money, they have nice pepper spray anti-intrusion devices i used to see advertised in SGNews, that would work as perimeter defense.

      Biggest thing with anything you do is YOUR OWN SAFETY. And always play with the triggering device APART from the flare/whatever for a while so you know how it works before actually hooking it up, being OVERLY cautious with ‘safeties’ in place if you are in any close proximity.

  • Stephen October 27, 2014, 12:52 pm

    I just searched EBay and could not find this item anywhere on the site. Could you please post a link to this item?
    Thanks

  • Mahatma Muhjesbude October 27, 2014, 8:53 am

    Excellent and important article, Paul, Mitigating the element of surprise can be a life or death advantage with warning–or the last disadvantage you’ll ever have if you’re caught unaware. And it’s always best that you know something is ‘coming’ a bit farther away than your doorstep. Being secluded and isolated has it’s good advantages but there’s one bad one in that if someone is sneaking up on you, it’s likely that there’ll be no one else to see them or stop them but you. To me, perimeter warning and defense is the second most important security factor right after your personal weapon. Depending upon your situation and money, you can stop just about anything. But minimal cost and simplicity like this is the ideal basic set up.
    You’d never believe how many enemy were ‘made’ and killed back in the days with just an empty pop can filled with rattling stones hanging on the perimeter wires.

    This really looks like a good ‘bang for the buck’ and well made to last. As a former 18-B, I learned just about everything there is to know at one time or another about ‘booby traps’ and perimeter security, and it did save our drunk and tired-ass lives on at least a couple occasions.

    They used to make something similar a long time ago that fired an off sized 12 Ga. round on a pull pin trip wire. If this company made a 12 ga. version of this nice little slick device that could fire all those specialty firework(crow air bursts), flares that go bang and are visible over trees, etc and pepper shot loads. Even smoke grenades would be ‘effective’ as a ‘confusion’ device and easily spottable for location at distance. I don’t think those fall under actual ‘illegal booby traps’ and would be interesting variables.

    The other thing is that a human’s forward visibility cone is usually several meters out ahead off his footsteps, unless he’s specifically searching a trail for a trip wire up close like point men in the jungle used to do. But a clear plastic fishing line will reflect sunlight at that distance and potentially be spotted. Whereas a flat black or brown, green, etc. will never be spotted until it’s too late.

    The other thing is the indigenous population of local critters will keep you constantly re-setting if you don’t think about it. So the ‘height’ of the trip wire is something to consider. Best height is just above where the average footstep can’t step ‘over’ it–which is about shin height. Anything higher might be noticed by an intruder’s downward vision cone. But the only way you’ll keep the deer from tripping your alarms is the put the wire at human neck level, which during the day time is usually easily spotted by human eyes. But at night it won’t be.

    • Administrator October 27, 2014, 9:26 am

      that’s great info thanks. I was thinking about using that green wire you can get from milsurp.

      • Russ October 27, 2014, 2:56 pm

        Ya good tips Mahatma Muhjesbude, thanks.

    • Chilco October 18, 2015, 12:58 am

      It’s not too hard to re-engineer this device or a similar home made one to shoot everything from a percussion cap to a firecracker or smoke bomb. You’ve got an ignition source, right? My best early warning alarm is a whistling bottle rocket that explodes on a trip wire system. I’ve had them last through a winter here in Idaho and that means they were buried in snow. Out of seven set 4 were triggered and 3 made it 4 months of some pretty nasty weather. As a matter of fact, the last 2, I accidentally tripped looking for them. Don’t use monofilament, it will catch the rays of the sun sometimes and it won’t last. Use very small braided fly fishing line. You can get it green or brown, it’s very strong and damn near invisible with the right background cover. It’s easy to make snares and trip wire alarms with a mousetrap. The 12 gauge shell sounds like a worthy experiment, I ‘ll check back on the progress if anyone cares. Hey, you gotta work with what you got, right?

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