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. With Meprolight, 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: No batteries - no switches - always ready for action Daytime confidence under low light conditions Totally integrated day/night operation Quick shooting in urban areas Rapid target acquisition Large field of view Self Illuminated power source