Abstract: A security grille (1) adapted to securely close off a window, but which may be manually released from within the building including the window while maintaining security preventing unauthorized access from the exterior of the building. The grille (1) is attached along one edge by hinges (2), or by a releasable mechanism, and is lockable in position by locking device (20) on an opposite edge. The locking device (20) may including locking bolts which protrude out through holes (21, 24 ) which engage holes (22, 25) within a surrounding frame (32). The grille (1) can comprise two portions (1a, 1b) joined at their mating edges by further hinges (23). The frame (32) is secured by bolt devices (26), or the like to the wall structure of the building surrounding the window to be protected.