Skull watch

Skull watch was a necromancy spell that created a watchful guardian that sounded an alarm when a living creature was detected. An older version of this spell had a much shorter duration but was otherwise practically identical in effect.

Effects
The primary material component of this spell was an intact skull and jaw bone from an intelligent creature. When cast, the spell caused the skull to become sensitive to life in a 20 ft (6.1 m) wide by 90 ft (27.4 m) corridor emanating from the eye sockets, as if the skull were gazing down said corridor. The skull could be positioned by resting it on a surface or it would hover in the place it was held as the spell was being cast. If any living creature entered the warded corridor, the skull immediately let out a piercing shriek that could be heard up to a quarter mile (400 m) away and was telepathically heard by the caster as long as he or she remained on the same plane as the skull. After the alarm was triggered, a hovering skull floated gently to the ground. The older version of this spell added a dramatic dying wail as the skull descended. The duration of this ward was only a few minutes for the older version, but a minimum of an hour for the newer version.

Stationary physical barriers, such as walls, were sufficient to block the gaze of the skull. The skull could be turned to look in a different direction, moved, or even destroyed without setting off the alarm, as long as the trigger condition was not met. For the older version of this spell, any of these actions resulted in the caster hearing a rumbling echo; the newer version gave the caster no indication unless the alarm was set off. Any silence spell or effect would muffle the audible shriek, but the caster would still be mentally aware that the ward was breached.

If the caster set more than one of these skull watch guardians, the mental awareness alone was not specific enough to distinguish which one was tripped because they all "sounded" alike inside the caster's head.

Components
Both versions of this spell had verbal and somatic components and required a complete skull (with jaw) of an intelligent creature that was not consumed in the casting and could be reused after the spell ended. The newer version further stipulated that it be the skull of a humanoid creature. The older version also required a thread and a bit of the caster's earwax.

History
This spell was published in "Volo's Guide to All Things Magical" and became generally known to the magical community.