Not all home laser tag sets provide vests in their kits, so for those, the gun itself is often both sensor and shooter. For sets that do include vests, if the gun has a sensor that can register a hit, then you may not need to wear the vests also.
Some laser tag sets will opt to use a headset rather than a vest which just means there won’t be any cheap hiding of the body in a match. It’s best to read the instructions that come with your set to see which parts do what.