Introduction: Perimeter Alarm, Trip Wire, Booby Trap

I have a building about 300 feet from my residence. This building is a shed that houses lawn equipment, snow removal equipment, a pickup truck and misc. tools and fuel. The shed was built for storage and is not easy to secure (there is a 1 foot gap between the side and the ground). It has no electrical power and is not visible from the residence. I needed a low cost alarm that would alert when the equipment is being disturbed. I have two dogs that alter when they hear loud noises such as a gun shot.

After doing some research I found that a 12 gauge shotgun shell fits in a 3/4 inch black pipe to make a make shift barrel. (the pipe is welded and the inter seam may have to be filed for the shell to completely enter he pipe) I also learned that the pipe is not strong enough for repeated shotgun blasts, so I decided to use just the primer as a noise maker and not use a complete shell with powder. I wanted to make an alarm not a pipe bomb.

I wanted a simple device to make, so I went to the home center and picked up the following items.

4 inch long 3/4 inch black pipe nipple

PVC 3/4 inch threaded female coupler to 3/4 inch glue fitting

PVC 3/4 inch to 1/2 bushing glue fitting

3 inch long 1/2 PVC pipe

PVC 1/2 inch glue fitting to 1/2 female threaded fitting

PVC 1/2 threaded plug

4 inch 1/4-20 bolt and nut

Spring .035 wire 6 turns per inch 3/8 diameter 3.25 inches long (this was just cut off a 12 inch length of spring)

8 penny nail (end blunted to reduce piercing the primer)

1/2 inch dowel 1 inch long wrapped with masking tape to make a slip fit in 1/2 pipe.

Pop rivet pin to secure firing pin.

All these items were purchased for less than $10, (researching the internet I have got the price to just under $5 each)

Step 1: Machining (hole Drilling)

There are 3 holes to be drilled

Drill an 1/4 inch hole through the center of the plug

Drill an 9/64 hole through the 1/4-20 bolt to secure the striker, the location is found by assembling the spring on the bolt and inserting it into the plug and then while holding in a vise with the spring fully compressed mark the bolt on the bottom of the plug. Grind a flat on the bolt where the hole will be drill. Using a vise on the drill press, align the bolt to the drill bit, a small ruler between the drill bit and the bolt will locate the center of the bolt by acting like a seesaw and when it is centered the ruler will be horizontal. Remove the ruler and drill the hole.

The last hole is a clearance hole in the dowel for the 8 penny nail.

Drill and 1/8 hole in the center of the dowel for the firing pin (nail)

Step 2: Glue Plastic Pipe

Now glue the female coupling, bushing, 1/2 pipe, and female coupling together.

Step 3: Preparing the Empty Shotgun Shell

Get a spent 12 gauge shotgun shell and remove the used primer.

Purchase a box of new primers, (available at sporting goods, gun shops, Bass Pro, Cabela, Midway USA, even some Walmart carry them with the black powder firearms ammunition)

Insert the new primer in the shell and press in place (an assist from a dowel and a mallet or a reloading press may be needed)


Primer only.

Step 4: Assemble Firing Pin, Striker, and Release Pin

Insert firing pin into 1/2 pipe.

Insert spring onto bolt and insert through hole in pipe plug attach nut to keep assembly together

Screw pipe plug into pipe assembly

Secure in vise and cock striker, insert pop rivet Release Pin

Attach cord or string to release pin

Insert primed shell into black pipe and screw onto plastic pipe

Mount to a fixed object near to the monitoring point with conduit straps

Run trip wire (string) using eye hook to change direction

Then wait for the alarm to be activated