An improved pyrotechnic cap which includes a plastic container having a quantity of pyrotechnic composition hermetically sealed therein. The cap is capable of being ignited by the radiant energy from an adjacent flashlamp to provide an audible signal of high intensity (e.g. 158 to 164 decibels at 25 centimeters). The improvement constitutes providing the composition with a quantity of desensitizing material (e.g. powdered polyethylene) which significantly decreases the cap's sensitivity to ignition by mechanical impact or crushing.