A novel way of keeping thieves out of dwellings and other spaces utilizes two interlocked, relatively nested doors which, when so interrelated, are in turn, separately locked as a unit within the door frame. Release from the exterior requires knowledge of a secret system of a push-button control which must be operated in proper sequence. Special, tamper-proof hinges, common to the doors, permit them to be hung in the door frame for separate swinging or movement as a unit. The interlock between the doors is releasable only from the inside and, upon such release, the outer door remains locked until separately released by the occupant.