9 Wearable Gadgets With Staying Power

Courtesy company/Joseph Wang
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These temporary tattoos made by Electrozyme measure the presence of lactate in the wearer's sweat. The measurements are then transmitted wirelessly to track the electrolyte balance and hydration level.

Electrozyme isn't the only group of researchers creating "smart skin." A team of scientists at the University of Tokyo have made an ultra-thin, flexible electronic circuit that can be worn as a tattoo.

Cost: Not available