Abstract: A fluid-actuated locking device for the doors of dwellings or offices or for armored doors having a plurality of tubes for the flow of a fluid supplied from a reservoir, which fluid may either be pressurized to operate a lock or may flow back through the tubes after the release of the pressure so as to allow the locking of the door; a presettable combination is provided to predetermine whether fluid will flow through the tubes thus allowing operation of the lock to unlock the door, numbers or letters being provided and usable in the presettable combination; the fluid is subjected to pressure by a pump to effect withdrawal of pistons from the locking once the preset combination has been set to the preselected combination; the fluid is fed to the lock by a valved manifold which also controls the back flow of the fluid from the lock to the reservoir and works in association with the presettable combination to unlock or lock the door; and locking of the door is accomplished by the action of springs in the lock an