this is a simple, cheap and quick trip wire using mostly pen parts and some other miscellaneous equipment and objects. I built this for fun but is well equipped for a more serious situation like paintball or any other games/sports where a trip wire alarm would come in handy :)
Step 1: Requirements and tips
To build this i used a large 2 piece pen that screws together below halfway,
i also found a huge spring from another pen, all others fail so find the biggest one you can
a lighter and a pin are required to melt holes in the pen to enable cocking and ventilation
a straightened paperclip works well as a pin to hold the firing pin in place
try to find a solid and heavy bolt with a flat end, this will be where the contact is made and the combustion happens, so make sure it is sturdy enough to withstand a small blast
i used a sharp and strong hook to secure the end of the wire so some pliers may come in handy
Step 2: How to set up...
I have used the cartridge from a .22 caliber bullet to protect my fingers when the device is cocked. When the holes line up, insert the pin to lock the firing rod. Place a cap on the end of the nail (i use a tiny amount of plasticine putty to prevent it falling off) and screw the pen together. fasten to a tree or peg using straps or tape. Once this is complete attach the wire and wait until it is triggered, it will make a loud pop when the wire has been tripped (remember to make at least four holes for smoke to come out, this will also increase the noise produced and prevent the pen from exploding). this can be used over and over again, just make sure you replace the spring regularly as the cap releases chemicals which speed up the oxidization process.
Have fun and be safe :D
P.s this can also be used as a crude ballistic knife/shank