Which accidental discovery led to the development of RFID technology now used extensively in retail inventory tracking?

Throughout history, some of the most transformative retail and product innovations have come about through unexpected discoveries or mistakes. These 'happy accidents' have revolutionized how we shop, interact with products, and understand consumer behavior. This trivia question explores one such pivotal discovery that changed the retail landscape forever. Test your knowledge of how serendipity has shaped modern commerce!

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Leon Theremin's espionage device that reflected radio waves to detect sound vibrations (1945)
Percy Spencer noticing a chocolate bar melting near radar equipment (1945)
Arthur Fry's failed adhesive that became Post-it Notes (1974)
Richard Jones dropping a tension spring that 'walked' instead of falling (1943)