The Mil-Spec Mepro M21 Self-Illuminated Reflex Sight is used and trusted by militaries and law enforcement agencies worldwide. It is specifically unique in that no batteries are needed. Illumination of the point of aim reticle is achieved by a fiber optic collector system during the day and by a miniature self- powered tritium light source at night.A large 30 mm display window allows the shooter to keep both eyes open for better battlefield situational awareness. The mount allows for fast attachment to rail-equipped firearms or AR carry handles. Also designed to work with a red-dot magnifier. Includes a neoprene protective cover.With Meprolight USA everything you aim for. Mepro M21 is the reliable choice. Designed and manufactured the highest military standards to assure years of reliable operation under all field conditions. With no switches no battery or other external sources of power the sight is always ready for action.Features / SpecsNo batteries - no switches - always ready for actionDaytime confidence under low light conditionsTotally integrated day/night operationQuick shooting in urban areasRapid target acquisitionLarge field of viewSelf Illuminated power source