Abstract: A door security system is used in conjunction with a lock such as a deadbolt lock having an "inside" located actuating handle, of the type used in hotel rooms, having a major and a minor dimensional axis. The security device has a baseplate that fits beneath the faceplate of the lock and which can be oriented during installation in relation to the shaped actuating handle of the lock. The baseplate of the security device extends eccentrically off center and supports a pivot post that carries a latch locking plate. The locking plate is pivotally supported on the pivot post, for pivotal rotation thereabout, and has an arcuate passage off-set from the pivot post, in use to receive the lock actuating handle. In use, with the baseplate installed beneath the faceplate of the lock and the lock handle rotated to extend the bolt, the locking plate may be rotated about the pivot post, swinging the arcuate passage over the lock handle in immobilizing relation therewith.