Discovering that your new designer handbag or gold watch is a fake is costly and annoying, and counterfeit medical devices or drugs could have even more serious consequences. But seemingly as soon as manufacturers develop a new method to ensure product authenticity, counterfeiters find a way to outsmart it. Now, researchers have created an “unclonable” tag that can never be replicated, even by the manufacturer. They report their results in ACS Applied Materials & Interfaces.