Abstract: An improved security cover for windows includes a metal frame dimensioned to fit within the window frame outside the conventional window, and key-actuated locking means visible and operable only from the inwardly directed side is provided in the metal frame for cooperating with the adjacent window frame structure to firmly but releasably retain the rigid metal frame in position covering the window. Suitable security means such as bars, metal grill work, or expanded metal are provided in the metal frame opening, and storm windows, screens, or the like may also be mounted in and supported by the metal frame.