Concealment Charm

"Look, Secrecy Sensors detect jinxes, curses, and concealment charms, don't they? They're used to find dark magic and dark objects. They'd have picked up a powerful curse, like the one in the necklace, within seconds."

- Hermione Granger.

Concealment charms (incantation unknown) are spells used to conceal inherent magical properties of objects from Dark Detectors.

In 1996, when Harry Potter speculated that Draco Malfoy had sneaked the cursed opal necklace by Filch's Secrecy Sensor, Hermione Granger said that Secrecy Sensors picked up concealment charms easily.

Appearances

 * Harry Potter and the Half-Blood Prince