This spell requires the complete skull (including jaw) of an intelligent humanoid creature. Once the spell is cast, the skull is set in midair facing a particular direction. The skull will then hang there in midair. The eye sockets of the skull define a path 20 feet wide by 90 feet long. Physical boundaries such as walls do limit that path.
Any living creature that enters the area of this path within the limitations of the spell activates the skull watch. The skull emits a piercing shriek that can be heard up to a quarter-mile away. In addition, the wizard who cast the skull watch is immediately aware that something has tripped the spell. Silence spells and similar magics can stop the audible shriek, but the wizard becomes aware of the event regardless of location, as long as the wizard is alive, conscious, and on the same plane. The skull can be moved from its position without activating it, as long as the individual does not step within the path.
The skull also can be destroyed. The skull has 1 hit point per level of the caster and an AC of 7. The skull makes no other attacks. The caster is not made aware if the skull is destroyed without the spell being triggered.
A wizard who has multiple skull watches operating will be unable to discern which has been tripped, as the "scream" and "mental awareness" are similar for all skulls created by this spell.
After being triggered, the floating skull sinks slowly to the ground and can be reused at a later time.
Notes: Uncommon spell from the Forgotten Realms setting. Known to be in the tome, Tidings of Conflict and Woe.