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 sights 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 for a range of 50ft. The dual sided N-Gage Activation Buttons provide a large, easy-to-find, bright red activation button, which emits a powerful (5mW) red aiming laser.