Meprolight’s battle-proven M21 reflex sight features a tritium-powered reticle that is aided by a fiber-optic collector. Still, under certain circumstances—such as when the user is aiming from a dark area into a strongly sunlit area—the M21 and similar sights can experience reticle “washout.” Inventor Chris Roenker has solved that problem with a low-cost, bolt-on enhancement in the form of his Reticle Enhancement Module 21 (REM-21). The unit, powered by a single CR2032 cell or two CR2016s, projects light from a diode onto the sight’s collector, and its intensity can be varied by an 11-position control knob. Battery life with the CR2032 is 106 hours of continuous use. Price: $29. Contact: M1BullPup; m1bullpup.com.