A security device for use with audio and video equipment installed in an automobile or other type of vehicle, such as a van or boat. The security device includes a module which is coupled to the equipment to be protected. The security device comprises an encoded security key which is plugged into a key receptacle to disarm and arm the module. The key includes logic for producing an encoded disarming signal and is of a size which can be easily carried on the person of the user. The module can be located at a space in the vehicle which is remote to the key receptacle thereby allowing otherwise inaccessible equipment to be conveniently secured from the passenger compartment of the vehicle for example. Without a proper encoded key, the equipment cannot be operated and is virtually useless if removed from the vehicle. To provide a further deterrent to theft, the module and/or equipment include a warning notice signifying the inoperative nature of the equipment without the key.