Abstract: The invention provides a restricting device for a closure including a vent hingedly connected to a frame, the restricting device comprising a plate (1,4) for mounting on a frame, an arm (7) for pivotally mounting on a vent and means for releasably interengaging the arm and the plate, wherein, in use, when the plate and the arm are interengaged, the closure can only be opened a predetermined distance. The means for releasably interengaging the arm and the plate comprise a resilient means (2) adapted to engage a locking pin (5). The engagement between the arm and the plate is released by means of a release means, for example a key (6,6?;6?), which is separate from the rest of the device. A preferred embodiment of the invention provides means (16,17; 18, 20) for preventing over-rotation of the key beyond a position in which the resilient means is in an optimum release position. The device is simple to use and has the advantage that it is detachable.