Used laser tag equipment is composed of a body shield which is infrared sensitive targets which, when "tagged" or "tazed", by another player will light up to denote a "hit". Your "weapon of choice" is an infrared emitting targeting device which is attached to the body piece. This way, you record how many hits you've scored and, whether you have been hit or not. The variety of designs of "weapons" available will blow your mind. From the simple hand-gun, to the very exotic "inter-galactic" versions.
The computerized electronics may be calibrated to ignore friendly fire, limiting the range of fire, as well as other features which mostly depend on the age of the user(s) and the complexity of the game desired.
There is even used laser tag equipment that has been manufactured for outdoor use, exclusively. This type of equipment requires a higher output of infrared light, due to the fact that you are using it in sunlight versus black lights.