Muggles' Guide to Harry Potter/Magic/Secrecy Sensor

Muggles' Guide to Harry Potter - Magic
Secrecy Sensor
Type	Device
Features	Detects dark magic
First Appearance	Harry Potter and the Half-Blood Prince

Overview

The Secrecy Sensor is a device that detects certain classes of Dark magic.

Extended Description

Hermione tells us that the Secrecy Sensor can detect "jinxes, curses, and concealment charms", and so are useful for detecting a reasonably wide range of Dark magic. They can be operated by the non-magical; the first time we see one, it is being wielded by Filch, who is a Squib. Hermione goes on to say that they are useless to detect love potions, because love potions are not Dark magic; and they can be concealed by putting them in perfume bottles, no Concealment charm is necessary.