The DS-121 Defender Series Accu-Guard Laser Sight by Crimson Trace is compatible with 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. Compatible with Glock Gen 3 17/17L/19/20/20SF/21/21SF/22/23/31/32/34/35/37/38 Gen 4 17/19/20/21/22/23/34/45 Gen 5 17/19/19X