The DS-121 Defender Series Accu-Guard Laser Sight by Crimson Trace fits GLOCK Full-Size and Compact pistols. The Defender Series sets a new standard in laser sight for GLOCK pistols by providing cutting edge design, superior technology, and an affordable price tag. The DS-121 features Beam Lock Adjustments so that the user can easily adjust laser sighting for both windage and elevation, and the unit is pre-sighted at the factory at 50 ft. The Dual Side N-Gage Activation Buttons provide a large, easy-to-find, bright red activation button, which emits a powerful (5mW peak, 620-670nm, Class 3R) red aiming laser..