Alastor Moody's Foe-Glass.
- "That's a Foe-Glass. Lets me keep an eye on my enemies. If I can see the whites of their eyes, they're standing right behind me."
- — Bartemius Crouch Jr., impersonating Alastor Moody[src]
A Foe-Glass is a type of Dark Detector. It looks like a mirror, but instead of a reflection it shows the enemies of its possessor. The figures appear as "shadows" but become clearer and more visible as the enemies get closer to the possessor.
Bartemius Crouch Jr. impersonating Alastor Moody had Moody's Foe-Glass in his office during Harry Potter's fourth year at Hogwarts School of Witchcraft and Wizardry. He said he's not really "in trouble" until he can see "the whites of their eyes". Later in the school year, after Cedric Diggory tragic death, it is revealed that Crouch's enemies shown in the glass are Albus Dumbledore, Minerva McGonnagal and Severus Snape.