To create an airsoft tripmine that doesn’t fire bb’s (thus it only makes a bang that will alert you as to where the enemy is) you could simply omit the bb from the bb tripmine plan. However, there is a far simpler way……
Crackers (the type you pull at Christmas not the kind that Jacobs make) omit a very safe loud audible snap sound, they can be disassembled very easily, and they are safe even if they go off in your hands.
Below is a diagram that shows how we constructed several tripmines that we have used over the years (we used to put them on one side of the bridge at Chobham to alert us to when the enemy were crossing).
Remember kids explosives can (and often do) KILL
CHIFF_MoA