A tamper-proof window unit comprising similar first and second quadrilateral centrally open frame members adapted to be mounted about an opening respectively on opposite sides of a door. Each frame member has a narrow elongated quadrilateral front panel extending generally in a plane parallel to the door and marginally about the door opening with an outer edge portion partially overlapping the door adjacent the opening. A small countersunk front to rear screw hole is provided in each side of front panel of a first frame member and the opening is spaced inwardly from the outer edge of the panel so as to communicate with the door opening. A narrow elongated quadrilateral integral flange extends along and projects rearwardly toward the door from an outer edge of each front panel. A second narrow elongated quadrilateral and generally L-shaped integral flange extends along the inner edge of each front panel with each L-shaped flange comprising first and second panels. The first panel of each L-shaped flange projects generally rearwardly from its associated front panel but at a slight angle of inclination toward the center of the door opening. The second panel projects from the rear or inner edge of the first panel outwardly with respect to the center of the door opening and in a plane generally parallel with the door faces and the front panels.