The invention relates to a device for restricting movement of a sash window relative to a frame, the window comprising: a sash including a pair of stiles, a channel disposed lengthways of one of the stiles; and the frame comprising: a sill, a head spaced from the sill, a pair of jambs and a frame slide track disposed lengthways of one of the jambs; the device comprising: a frame-mounted slide member for slideable engagement with the frame slide track for lengthwise movement relative thereto; a sash slide member for slideable engagement with the channel for lengthwise movement relative thereto; a first arm pivotably connected at one end to the frame-mounted slide member, and pivotably connected at its other end to the sash slide member; and a second arm pivotably connected at its one end to the frame-mounted slide member, and at its other end providing for connection to the sash; such that in use the movement of the window relative to the frame is restricted by the first and second arms.