In this video by MrGear, he demonstrates how to make a strike-ball trip-wire alarm. If you are planning a campfire or special effect, this method might come in handy for you.
A trip-wire alarm is one of the most basic security systems, designed to be easily installed. The conventional trip-wire security system consists of a wire stretched across a path. Once someone trips over the cable, it triggers an alarm and trap, or some other kind of signal would alert you of movement from intruders.
To make the DIY trip-wire alarm, first, he takes a wooden clothespin and pulls it apart. Then, he takes an AA battery and glues it to one-half of the clothespin, on the inner part. Next, he takes black and red wires and ties each of them to the pointy ends of metal thumbtacks. He then tacks on the wires to different halves of the clothespin, the red wire on the half with the battery stuck to it.
He glues the free tip of the red wire to the positive end of the battery and the tip of a cut black wire on the negative end of the battery. Using some black and wires stuck together with a clay paste made from matches, he demonstrates how the clay ignites and burns when the wires are connected to the separate ends of an AA battery.
The clay paste is the part of the matchstick that burns. You scrape it off from a couple of matchsticks, ground it into powder, and make it gooey by adding liquid. When you place it on the wires, it will ignite if a current passes or if you light it with matches.
After the simple demonstration, he applies the concept to the contraption he has been building, finishing the project by pinching a wire between the clothespin’s teeth and running its length from tree to tree to see what happens when someone trips it. As expected, it ignites the clay paste.