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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
user81097
As @allObjects says, adding one of those ICs would be perfect. It's far more secure than using an EEPROM since you can't just copy its contents.
Another (cheap) option is to add a OneWire device - those have 64 bit unique IDs that are set at the factory. The only way to duplicate them would be to make your own fake OneWire device with a microcontroller, which I doubt anyone copying your device would be willing to do.