Some Dark Detectors, 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.
Known Dark Detectors
Usages
Alastor Moody
Alastor Moody seems to own quite a bunch of these. This is probably because of his cautious nature. They were used by Barty Crouch Jr when he was impersonating Moody.
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.