Tamperproof security door lock

Abstract

A mechanism which may be added to existing conventional type cylindrical door locks at the time of manufacture thereof or to such locks already in the field with just a slight modification of the existing lock. The structure of the added security mechanism blocks the throw of the latch bolt and at the same time blocks the retractor to positively prevent opening of the lock by key, turning of the knob, or tampering with the latch. The security device is tamperproof as it is inserted into the interior of the cylindrical lock and can only be disengaged to allow entry from inside the building structure. The lock cannot be opened from the exterior of the door when the security device is engaged, by any conventional method or tampering. The mechanism includes a shaft or rod having an actuating knob on one end thereof which is removable for installation of the device and a guide and alignment pin together with an operating and blocking shaft with projecting wings on a plate member for engagement and disengagement with the latch of the conventional cylindrical lock. A special retaining and bias spring is mounted in appropriate holes in the lock device. A modified cover plate is also required which has a diamond-shaped aperture of sufficient size to receive the rod shaft, guiding pin, and retaining spring member.

Dependencies are inferred from the claim text.