This groundbreaking new design incorporates the laser into the rear sight. Compact size and revolutionary performance make the new Rear Sight Laser (RSL) the most extraordinary system LaserLyte has ever produced. As easy to install as it is to operate, the new RSL offers a high-power laser with the benefit of not having to replace existing grips, internal stock parts, or holsters. The activation switch is a strategically placed button at the back of the slide that is easily activated by the thumb in a normal shooting position for left- or right-handed shooters. Press the activation switch once for a constant "on" mode, twice for "pulse" mode, and three times to deactivate the laser. Small LED indicator on the back of the laser indicates which mode is engaged. Constructed from MIM 4650k nickel enriched high-carbon steel, the same material used for most heavy-duty gun parts such as iron sights, hammers, and levers. It is also black oxide, bead-blasted for a non-reflective finish. Fits all Glock pistols. When mounted onto the pistol, the RSL will fit all Level 1 and 2 holsters. Runs on four 377 batteries for 1 hr. of continuous use or 2 hrs. on pulse. Range at night: 500 yds. Measures 0.85"H x 1.05"W x 0.35"H. Weighs 1.2 oz. One-year limited warranty.