|"There are plenty of eye-witness accounts. Just because you're so narrow-minded you need to have everything shoved under your nose before you–"
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The Intruder Charm (incantation unknown) is a spell which detects intruders and sounds an alarm, the magical-equivalent to a burglar alarm. Horace Slughorn used it on a Muggle-owned house he stayed in temporarily in 1996 but did not hear it go off when Albus Dumbledore and Harry Potter arrived because he was in the bath.
Behind the scenes
- The Caterwauling Charm could be a long-range version of this charm since it was loud enough to alert the Death Eaters and all the villagers when the trio came into Hogsmeade.