The Viridian Reactor R5-R Gen 2 red laser sighting system is easy to install and blends seamlessly into the trigger guard for invisible profile and smooth draw. Viridian's red lasers utilize a 635-650nm laser wavelength to generate the brightest, sharpest red dot possible. The gen 2 models feature a Instant-On ambidextrous, inside the waistband (IWB), custom fit holster with INSTANT-ON activation. This model is compatible with Smith and Wesson M&P Shield 9/40.