 Most purpose-made military booby-trap firing devices contain some form of spring-loaded firing pin designed to strike a percussion cap connected to a detonator at one end.The detonator is inserted into an explosive charge—e.g., C4 or a block of TNT.Triggering the booby-trap (e.g., by pulling on a trip-wire) releases the cocked firing pin that flips forward to strike the percussion cap, firing it and the attached detonator; the shock-wave from the detonator sets off the main explosive charge.