The Arrow K.R.D has been designed to provide users with the opportunity to overcome what has often been a major stumbling block towards increasing door security - namely, that fitting door chains can prevent entry by authorised personnel in the event of an emergency; very important especially where elderly persons in sheltered units are concerned. The Arrow K.R.D. accepts interchangeable cores which can be masterkeyed, allowing authorised personnel to release the door chain by masterkey and occupants by their own individual key. Where a complex is already utilising an interchangeable core masterkey system, the Arrow K.R.D. will be able to accept a core to match the existing cylinder core so that no additional keys will be required. Alternatively the Arrow K.R.D. can be provided with Arrow cores/keys as a ‘stand-alone’ masterkey system.