I have this Streamlight M3 Tactical Illuminator light. The light mounts right on the rail of a pistol. I have this light mounted on my Model 23 .40 caliber pistol. This light comes in handy for making entrances into dark buildings or homes that we get called to for possible burglaries or other situations that may be better off leaving the lights out resulting in the bag guy knowing your location. This light can also act as a back up light if your regular flashlight dies on you. This light has a feature switch that allows you to turn the light on steady or just turn the switch to the on position for as long as you hold it and when you release the switch it goes off, could be on for a matter of second if you desire. This light operates of 2 lithium batteries like the ones used in some common cameras This is definately a nice tool to have in the law enforcement field. It may not be used everyday but nice to have if you need it.