1. A print engine comprising at least one print controller and at least one associated authentication device, each authentication device having a processor, non-volatile memory, an input for receiving power from a power supply and a power detection unit, wherein each authentication device is configured to enable multi-word writes to the non-volatile memory under control of the associated print controller, wherein the processor is configured to control and trim the amount of power supplied to the input to predetermine a threshold at which operation of the authentication device is established; and the power detection unit is configured to monitor a voltage level of the power supplied to the input, and in the event the voltage level drops below the predetermined threshold, preventing subsequent words in any multi-word write currently being performed from being written to the memory.