Just shake the flashlight, and it shines. Crank the radio's handle, and it plays. Unlike earlier generations of human-powered electronics, which quit the instant you did, a new breed stores your muscle energy in springs, batteries and capacitors that provide lasting returns.

Freeplay Energy in London has sold more than 2.5 million hand-cranked radios and flashlights since 1995. In its original products, turning a crank wound a tight 33-foot steel ribbon, which slowly uncoiled. In its new line, the crank turns a mini transmission that drives an alternator to charge onboard batteries. Thirty seconds of human effort will yield 40 minutes of play or eight minutes of light, and the products will be one fifth the size and weight, addressing a primary consumer complaint: human-powered electronics tend to be big and heavy.

This article was originally published with the title Crank It Up!.

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