Abstract: There are provided security devices (1) for restricting the movement of a door. A device (1) comprises a blocking member (3) for extending into the path of the door and is carried by a housing (5). In use, the blocking member (3) can move between an active position in which it restricts movement of said door and an inactive position in which it does not restrict movement of said door. Also provided are door assemblies and methods of installing security devices and of operating security devices.