Auspex

An auspex is a short-ranged scanner used by Space Marines to detect hidden enemy troops. If enemy infiltrators set up within 4D6" of a model with an auspex, then that model is allowed to take a 'free' shot at them (or sound the alarm in a Raid scenario). If the model is part of a unit then the whole unit may shoot. These shots are taken before the battle begins, and may cause the infiltrators to fall back. The normal shooting rules apply.