Locking devices that may be used with product display hooks, cabinets, and drawers are provided. A locking device according to one implementation comprising a housing and a shell. The housing includes an outer wall that defines an interior. The housing further includes a channel extending at least partially through the interior of the housing. The shell includes a projection. The shell is at least partially disposed within the interior of the housing and is moveable in a longitudinal direction within the interior of the housing. In an unlocked position, the projection is biased away from the first channel. In a locked position, the projection is maintained in the first channel.