Level: Cleric 3, Sorcerer 3, Wizard 3
Components: V, S
Casting Time: 1 standard action
Range: Personal
Target: You
You gain a perception of the forces of magic and can sense when magic is being manipulated by a spellcaster. You gain a +5 competence bonus on Spellcraft checks made to identify a spell as it is being cast.
If you have at least 5 ranks in Spellcraft, you are also able to sense the use of any spell or spell-like ability within 100 feet, so long as you have line of effect to the caster. With a Spellcraft check (DC 15 + spell level) you can even ascertain the spell being cast.
This determination happens quickly enough that you can attempt to counter the spell as a free action. Counterspell attempts are otherwise handled normally, and you can counter the spell even if you do not have line of sight to the spellcaster. If you counter a spell in this manner, the battlemagic perception spell ends immediately.
Source: Heroes of Battle, page 125.