Abstract: A security device for a window or other opening in a wall structure, such as a basement window, for preventing unauthorized entry therethrough. The device has an extensible bar adapted to extend across the window from side to side, and which is pivotable about one end between an initial position extending outwardly from the wall structure and a security position extending across the window. The device includes a locking bracket adapted for mounting on the wall structure adjacent the window or on the window frame itself and means such as a combination lock for releasably securing the other end of the bar thereto. On the opposite side of the window is a pivot bracket, also mounted on the wall structure or on the window frame and adapted to receive the pivot end of the bar. The bar is pivotally connected to the pivot bracket by a removable pivot pin that cannot be removed when the bar is locked at its other end to the locking bracket.