Spell Sense

A wizard who casts spell sense instantly becomes aware of all spells as they are being cast in a 25-foot radius around him, as well as the nature of the magic: the general effect of a spell being cast, level of the spell, whether its power originated from a magical item, etc.

The wizard can tell when another spellcaster in the area of effect begins casting a spell, possibly allowing him to react before the new spell takes effect. This detection is possible only if the other spellcaster is inside the 25-foot radius, regardless of where the spell will take effect. Spell sense does not inform the caster of magic that took effect before its casting.