I know Industrium Conflict isn't finished and that all new weapons are denied before the first release.
What I suggest isn't really a weapon, and I don't think someone already think about it.
The Snitch (Don't know if it's the good word, I'm French, and using Google Translate ^^) would be an item that when charged or partially charged, would permit you to see where it is. (With x, y and z as for using F3, I do not speak about GPS ...). It would be a part of I-Conflict
Then, you could drop it on the ground , and if a player, without seing, take it in his inventory, you could follow him during something like 15 minutes. (Don't know for the time, maybe more, counting the time needed to be taken by a player)
Also, it would be awesome on PvP servers, in order to follow oponent up to their hidden base
Recipe Idea:
(Where = Redstone, and = RE Battery)