Unleash your inner Rambo, with this trip wire boobytrap,
pulling the ring out of the end releases a hammer that detonates a snap cap from a cap gun.
only requires 3 small parts, a rubber band and come caps.

This can be strung across a doorway to surprise your unfortunate family,
used to anchor important objects or attach it to the inside of a locker.

V2 now added with some iterative improvements.

Printing
standard print settings will do, orientate as provided in the files.
Note that the long orange part has a built in support in the bottom, this will easily break off by hand.

How to assemble (colours reference photos)
Insert the yellow hammer goes into the orange body as shown, but it does not go in via the end as youd expect, it goes it through the open side, slide the hammer part in first, the sides of the opening flex out enough for you to feed it in sideways like this, once inside it will be locked inside but still slide up and down within the body.

To install the elastic you need to find an elastic band who's maximum stretch is about the same length as the orange body, it may be easer to loop over a longer thinner band.
push the yellow hammer down far enough to see the circle in the middle of it.
one end of the elastic band hooks around this.
To attach the other end use a short loop of string through your rubber band loop, and feed that through the bottom of the orange part, this allows you to pull the rubber band through that gap. It goes over top of where the caps go and then hooks onto the back of it, you can then pull the string out.

Optional parts
The smaller ring isn't strictly necessary, it just gives a more flexible attachment point to the rear, but there is already a strong eyelet there so up to you.
To use, you hold it in place and then feed a toothpick through the main body and the small ring.

How to use
once assembled with the rubber band in place, the yellow hammer should want to pull down to contact where the snap cap goes. make sure this slides freely, you may want to work it back and forth to ease it up or add a tiny bit of silicone oil but this shouldn't be needed.
Using your finger pull the yellow hammer back as far as it will go, this will make the two forked ends poke out of the tube, fit the diamond shape of the larger ring into this and allow the fork to pull it into the tube, this will lock it in place.
Place a cap on the nipple inside of the tube.

using the square hole at the bottom tie it to something solid, then tie the ring to a string going across a door etc. when the ring is pulled out it will release the hammer and set off the cap.
note that the blast of the cap is directed out of a trumpet going out of the side.

Sensitivity
if pulling the pin out is too stiff for your uses, you can make it easier by using a weaker elastic, so long as its still strong enough to set of the cap.
You can also cut down the corners of the pull out ring, just don't take off too much or it won't hold reliably.