|Although this article is based on canonical information, the actual name of this subject is conjectural.|
- “Thespia, we walk in shadow, walk in blindness. You are the protector of the night. Thespia, goddess, ruler of all darkness - we implore you - open a window to the world of the underbeing. With your knowledge, may we go in safety. With your grace, may we speak of your benevolence.”
- ―Willow Rosenberg[src]
The Demon Locator Spell was a spell that helped to locate the demonic energy in the area. The spell required an invocation to the goddess Thespia, a map of Sunnydale, candles, four crystals and a powder crushed in a mortar. When the potion was mixed, Thespia called and the powder was blown, it created a mist on the map over the parts where the demons were. It displayed different colors for different breeds.
In 2000, when searching a Polgara Demon, Tara Maclay, under the belief that she was part-demon, sabotaged the spell to avoid Willow from seeing the map indicate her. Many month later Willow suggested redoing the spell to Tara to locate Glorificus, still not knowing that she was, in fact, a goddess. But Tara feigned that she was tired, under the pression of her own family's return in her life.
In 2002, after her return from the magic cure in England, Willow redid the spell with Anya Jenkins to localise the demon Gnarl. However, the map burned because of a massive concentration of demons localized in the Hellmouth under the recently renovated Sunnydale High School. Willow also used this spell to localize the First Evil and a captured Spike.
A variant to locate humans existed as well. Willow used it one time to locate Dawn Summers and Anya under the charm of R.J. Brooks's jacket, and to find Buffy after she was rejected by her friends. She later tried another variant to locate Angel's soul, blocked in Muo-Ping and hidden by Jasmine.