Crimson Trace DS-121 Defender Series Accu-Guard Red Laser Sight for GLOCK Full-Size and Compact Pistols POWERFUL RED LASER: Features a 5mW peak, 620-670nm, Class 3R visible red laser - the brighest beam allowed by law. N-GAGE ACTIVATION: Ambidextrous Tap-On / Tap-Off Push Button Controls for immediate laser activation from either side of the unit. OVER TWO HOURS OF BATTERY LIFE: Powered by one 1/3N Battery (included). FITS Glock Third Generation 17, 19, 20, 20SF, 21, 21SF, 22, 23, 31, 32, 34, 35, 37, 38 GEN4 17, 19, 20, 21, 22, 23, 34, 35 GEN5 17, 19 EASY INSTALLATION: User installed- no gunsmithing required. Factory sighted at 50 feet, but is fully user adjustable for Windage and Elevation with provided tool.