You can automatically detect any illusion with an auditory component for what it truly is. No Will save is required, and you don’t have to interact with the illusion (but you must be able to hear its auditory component).
Varies. Every time you have a chance to hear something in a reactive manner (such as when someone makes a noise or you move into a new area), you can make a Listen check without using an action. Trying to hear something you failed to hear previously is a move action.
A half-elf has a +1 racial bonus on Listen checks.
A sleeping character may make Listen checks at a –10 penalty. A successful check awakens the sleeper.
A character can use Listen to notice the presence of an invisible creature (generally opposed by a Move Silently check). If the character beats the DC by 20 or more, he or she can pinpoint the location of the invisible creature, though it still maintains total concealment from the character (50% miss chance).
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