A data storage and processing device is reversibly attachable to a selected member of a set of appliances. The device includes a data storage medium and a processor. Each appliance includes appropriate functional components, a power source and a user interface. The device receives power from the attached appliance. Commands for operating the attached appliance are stored in the data storage medium and are executed by the processor in response to user instructions received from the attached appliance in order to operate the functional components. Preferably, the device receives power only from the attached appliance, and the functional components are operated, in response to the user instructions, only by the device's processor.