Invisibility Alarm

Standard Action | V, S, F/DF | Close | 20 ft radius
10 Minutes/level | None | No
This spell functions as alarm, except it is triggered only by invisible creatures entering or leaving the warded area. The spell has a different mental alarm depending on whether the invisible creature is entering or leaving the area. This spell does not aid you in sensing or pinpointing the location of an invisible creature within the spell's area.