This is the Israeli-built "Beam Hit" system. http://www.needspace.com/weblog/images/190-110_advertisement-shades.pdf You drop a plastic arbor matching the bore of your weapon down the muzzle. This screws into a battery-powered laser head. This unit senses the fall of your weapon's hammer and emits a brief burst of laser light on impact. That beam is picked up by a target with an integral digital counter. You can set that target to "ring" when you score a hit. This system works very well with revolvers and double-action automatic pistols but still gives acceptable service with single action weapons. You can practice in your bedroom or living room without driving other people crazy or inviting unwanted attention. I've read that far more advanced models, with targets using computer animation, are used by police and military services around the world.