The LaserLyte Rear Sight Laser is a new laser design which has the laser integrated into the rear sight. The sight is easy-to-install as you do not have to alter any internal parts or the grips as you do with many other laser designs. The Rear Sight Laser fits all Springfield XD and XDm models and is constructed of steel for high durability. Includes four #377 batteries (commonly used watch batteries) which provide up to 5 hours of runtime when constantly on, or up to 10 hours if used in pulse mode. Will also fit Sig Sauer Models 225, 226, 228, 239 & 2009.