Which scientific technology is primarily used in cutting-edge retail smart shelves that can automatically detect inventory levels without RFID tags or visual cameras?

In the intersection of retail technology and science, smart shelf systems are revolutionizing inventory management. These systems use various scientific principles to track products, monitor inventory levels, and even interact with customers. But how well do you understand the technology that powers these innovations? This trivia question explores the primary scientific technology enabling the most advanced smart shelf systems currently deployed in major retail chains.

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Quantum resonance scanning that detects molecular signatures of products
Weight-sensing load cells combined with machine learning algorithms to identify products by mass distribution patterns
Infrared spectroscopy that identifies products through their thermal signature
Ultrasonic echo-location that maps the presence and position of items on shelves