This Nuprol tactical RIS mounted torch takes 2 CR123A batteries (not included) and is activated using the ambidextrous lever on the back of the torch. Either twist the lever to toggle on or off, or press the lever in to turn on momentarily. The light and laser are selectable with a dial round the unit. You can select either safe, light only, laser only, or light and laser. This should fit on most railed pistols or 20mm RIS rifles.