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
Harry Potter owned two sneakoscopes throughout his Hogwart's years. The first one he got from Ron in 1993 for his Birthday. In 1997 Hermione gave him a new one for his Birthday, as his old one was cracked and worn out.