Category
The Garou is able to sense the presence of magic: Garou rituals, Gifts, Mage Spheres, Vampiric Thaumaturgy, and other assorted phenomenon. The Garou will get a general idea of presence and strength, as well as basic information (ie, whether it was a Mage Sphere or Garou Gift, but not which Sphere or Gift).
System
The Garou rolls Perception+Enigmas (diff based on the amount and subtlety of nearby magic). Each success lets the Garou locate magic in a 10' radius.