What innovative product design feature did Sony engineer Nobutoshi Kihara specifically create for the original 1979 Walkman that was revolutionary at the time?

Sony's iconic Walkman changed how we consume music forever, creating the foundation for today's portable music industry. This product design milestone represents one of the most significant innovations in consumer electronics history, blending technology with cultural impact. Test your knowledge about this revolutionary device that transformed music from a stationary experience to a personal soundtrack for everyday life.

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The ability to record audio directly onto cassettes
The iconic 'hotline' button that lowered music volume and activated a built-in microphone for conversation
A solar-powered backup battery system
Water-resistant casing for outdoor use