Abstract: Multiple embodiments of a security lock mechanism being adapted for both deadlocked and slam-lock operation are disclosed with different combinations of features including a housing, a movable locking bolt, a rotatable cam having a pin engaged with a slot in the bolt and a centering device such as a remote drive unit or double-acting spring mechanism coupled with the rotatable cam by a lost motion coupling for facilitating slam-lock and deadlocked operation of the security lock mechanism. With the remote drive unit being a pneumatically operated cylinder and piston, the piston is preferably of split construction to facilitate overriding operation of the remote drive unit, for example, by a key.