Abstract: The invention relates to a supplemental locking device for panel type doors which are mounted in a frame having top and bottom members and where one panel is adapted to open by sliding with respect to the other into a position adjacent the other door panel. More particularly, the apparatus of the invention includes a vertically disposed mounting post attached to the top and bottom door frame members and having a rigid bar pivotally attached to the mounting post so as to abut against or lock onto the handle or other part of the frame of the movable door so as to prevent the movable door from being open when the locking bar is perpendicular to the mounting post and in contact with the sliding door's handle.