Some Dark Detectors as Foe-Glasses and Sensors.
Dark Detectors are objects than can be used to detect lying, concealment, or even when Dark wizards or one's enemies are around. However, they should not be relied on too much, as they can be fooled.
Examples of some Dark Detectors are:
Usages
Alastor Moody
Alastor Moody seems to own quite a bunch of these.
Dumbledore's Army
When Dumbledore's Army was formed in [[1995] there were various Dark Detectors in the Room of Requirement when it served as the D.A.'s Headquarters.