An example with good ideas of an Arduino Laser Tag gun is given here.
They use a different Arduino but the series of 3 articles by Duane O’Brien gives almost everything you need to make a system with a few mods for the Arduino UNO and a sound module for realistic game play.
Science Club – Victor Harbor, South Australia
A Science, Technology, Engineering, Maths, Social, Enterprise and Learning club for school kids, that meets weekly at Encounter Lutheran College Victor Harbor.