Perimeter Watch

Perimeter Watch (Abjuration)
Level - 3
Duration - Special
Casting time - 1 turn
Area of Effect - 20' radius sphere
Range - 0
Components - V, S, M
Saving throw - none.
This spell establishes a circle around the caster (and their encampment) and alerts the caster when someone has entered this circle (who did not previously exit). The spell lasts until the next setting or rising of the sun. It also gives the caster a general idea (within 90 degrees) in which direction the perimeter was broken. Perimeter Watch can detect creatures of one hit die or larger, or multiple creatures of less than one hit die. The perimeter, once broken, will only remain in effect for one round per level of the caster. Note that this spell will awaken the caster if necessary, but will not interrupt spellcasting in progress. The material component is a bit of gold wire tied around a dog's tooth and the caster must walk the perimeter while casting the spell. The spell can be cast in a smaller area if desired.