Abstract: A door-locking device is described including a plurality of locking bars drivable to a locking position projecting from the sides of the door into the door frame by means of a rotatable drive gear and a plurality of gear-cam segments, one for each locking bar. Each segment includes gear teeth formed on a first portion of its outer circumference meshing with the teeth of the drive gear, and a cam surface formed on a second portion of its outer circumference engageable by a cam follower carried by its respective locking bar. The locking device further includes a key-operated locking cylinder and an overlying protector plate having an opening covered by a disc formed with the key slot, the disc being yieldingly secured to the protector plate to thereby prevent a drill from penetrating same into the lock cylinder.