Tell your player that it works the same as "Detect Evil" does for a paladin. To the distaste of paladins everywhere, its not an "always on" ability, but rather, something they have to spend an entire round concentrating on.
Now, as a DM with that character in my world, I would certainly use it for plotting. "As you step into the Chamber, the strong aura of evil threatens to overwhelm the paladin, and the mage stops and stares: he has never seen a magical aura so powerful."
'course, you better have a good encounter to back that up with! ;-)
Now, as a DM with that character in my world, I would certainly use it for plotting. "As you step into the Chamber, the strong aura of evil threatens to overwhelm the paladin, and the mage stops and stares: he has never seen a magical aura so powerful."
'course, you better have a good encounter to back that up with! ;-)
