kno one forwarded me a link to a diy lazer tag system that is off the hook.
MilesTag uses a digitally encoded signal allowing differentiation between up to 32 players and 7 teams, and supports a wide range of weapon types, including mines, area-denial and even non-conventional weapons. Damage inflicted by each weapon is scalable, and the performance of each weapon is fully configurable (rate of fire, ammo capacity, reload time, etc.).
the trogdornator (pictured above) really caught my eye. source and schematics are included so you and your friends can get together and build you own game. but make sure to pick your friends carefully — they must have courage, cunning and the ability to hack.