sunshadow21
Explorer
That would make a 3rd level spell easily circumvented by a Cantrip/Orion, and go a ways toward rendering a few spells and abilities moot. I'd say no, but I'm far from a guru.
I wouldn't say easily. The person using detect magic still has to concentrate, and if the invisible friend is moving around too quickly, could still lose track of him without too much effort. Against anybody else and or in a place with other sources of magic, it's even harder because the auras will blend together, requiring the caster to take even longer to pick out individual auras; lastly, you have to remember, detect magic doesn't give you the spell, it just gives you the school, and even that technically requires a spellcraft roll. If your friend with invisibility is in a room where an enemy wizard has cast an image spell, all you'll see is two illusion auras, with no immediate way to tell them apart. I'm not a judge, but I'd probably allow it simply because if they can actually pull it off after all of those constraints, they've earned it.