Human-presence-revealing Spell

Homenum Revelio is a charm which reveals human presences in the surrounding environment. The spell indicates a body by a marker, the appearance of which is yet unknown, but which can be felt by the target as something "swooping" low over him or her.

In 1997, Hermione Granger used this spell at Number 12, Grimmauld Place after escaping pursuing Death Eaters. Later that year, Death Eater used this spell to located Harry Potter at Xenophilius Lovegood's house.

Etymology
The incantation itself is a variation of "hominum revelo", the proper Latin for "I reveal a person".

Behind the scenes

 * J.K. Rowling stated that Albus Dumbledore could cast a wandless Homenum Revelio charm. This is the reason he was able to know Harry was present even while under the Invisibility cloak.