Abstract: A detachable guard or cover for preventing access to the keyhole of cylinder type locks in the face of a wall or locked door of a tool cabinet is combined with openings in the wall on each side of said keyhole. The guard comprises a generally U-shaped body having a pair of anchor legs joined at one end by a shouldered rivet. The free terminal end of each leg has a right angular tongue which fits into one of the openings in the wall when the guard straddles the keyhole to anchor the guard against the rear face of the wall. A locking leg journalled on the rivet fixes the guard when in closed position. The anchor legs and the locking leg have holes, which register when in closed position, to receive the shackle of a padlock. Alternatively, a lock set or cylinder lock may be built in to the anchor legs, with its pawl positioned to immobilize the locking leg until turned by a key to unlock.