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. How to make a TRIP-WIRE ALARM 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.