If you carry a full size flashlight, like the Streamlight SL-20X LED or SL-20L, the "stock" cap alone will not break glass (see our videos). There is no way you can break a window with these flashlights without causing damage to your expensive light or injuring someone from flying glass. Attaching Bust A Cap® to your flashlight will insure that it will break glass with just one tap and not damage your equipment.. . Warning: Please remove the o-rings from the old cap and put on your new Bust a cap to insure that your light remains water tight.