Camp Ward spell

Camp Ward
Spell Level: M2
Range: 30' Radius
Duration: 2 hours/caster level

This spell acts as a magical tripwire. Mages cast it on a central area, typically before going to sleep, and the spell helps prevent them from being surprised or ambushed at night. Whenever a creature with hostile intent comes within 30 feet of the spell focus, the mage is immediately warned, and will even wake from a normal slumber. The spell gives a general direction of the impending threat, though not a detailed description of the assailants, only that they exist.

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Any comments or suggestions are welcome. I think level 2 fits the spell, but it's a bit of a guess. I'm tempted to make the duration a flat 8 hours instead of variable.