Which revolutionary product design feature, introduced in 2007, eliminated physical buttons and created an entirely new category of consumer electronics?

The history of product design is filled with revolutionary moments that changed how we interact with everyday items. Some design innovations were so groundbreaking they transformed entire industries and consumer behaviors. This trivia question focuses on a pivotal design decision that created a billion-dollar product category. Test your knowledge of revolutionary product design history!

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The iPhone's multi-touch interface
The Kindle's e-ink display
The Dyson Air Multiplier's bladeless fan technology
The Nest Learning Thermostat's adaptive temperature control