Abstract: A device for deterring theft of an electrical or like appliance having an operation controlling microprocessor, including signal receiving means (2) connected to the microprocessor and adapted for connection to a power supply, first programmed means enabling the appliance microprocessor to disable the appliance, second programmable means separate from the appliance and including a microprocessor controlled signal generating means (1) for generating setting and resetting signals for transmission to the receiving means and operating to enable the first programmed means to render the appliance inoperable when power to the appliance is disconnected, said second programmable means being programmed to include an automatic reset routine which is activated by the restoration of power to the appliance to send a resetting signal to the appliance microprocessor to reset the microprocessor to an operative state whereby automatic resetting occurs in the event of power failure event.