Abstract: A keyhole barrier system for use with tumbler locks containing a keyway and a plurality of tumblers. The system contains a keyhole block having both retention and signaling portions. The retention portion prevents removal of the keyhole block from the lock by providing a locking surface for the lock tumblers. The signaling portion extends outwardly from the keyway preferably substantially parallel to the retention portion. The system can further include an extractor having both insertion and handle portions. The extractor facilitates removal of the installed keyhole block by raising the tumblers locked against the keyhole block. Further, the handle portion and the signaling portion can form a retraction aid to facilitate removal of the system from a keyway.