Skull of Warning
Description: The vampire takes an intact human skull and cleans it thoroughly, painting its eye sockets and teeth with her own vitae. She then impales the skull on an iron spike and places it near the entrance of her haven.
System: If the ritual succeeds, the skull stands silent perpetual vigil. Should any being other than the caster or undead minions belonging to the caster enter the room, the skull’s jaw drops and it lets out an unearthly howl of rage and pain. This sound awakens even a vampire sleeping during the day, although she must then struggle to stay awake normally. An enchanted skull continues shrieking until the intruder dies or leaves, or a number of minutes pass equal to the successes rolled. A single skull can serve as the focus of this ritual any number of times.
Reference: Players Guide to the High Clans - Mortis Rituals - Page 199.