Unaware (Quality)

A weapon with the "unaware" quality may only be used against an opponent who is either helpless or who has no knowledge of your location before you attack. Only a stealth check greater than the opponent's perception check can grant the unaware status. Note that even invisibility doesn't make you silent, and foes get a perception check to notice you (albeit at –20 to the roll, per the standard invisibility rules). See the Stealth skill page for more information.