Do you know your 'sweat score'? The rise of hydration tech

Flouris is a little sceptical of sweat-sensing. Referring to various unnamed devices that analyse sweat, which he has evaluated in the lab, he says, "Most of these products that we've tested do not show the level of accuracy that you would expect." The results of his experiments are as-yet unpublished. Sweat sensors, Flouris suggests, work best when worn during long bouts of physical activity – such as a marathon. But they struggle when the exertion is more varied and intermittent. Think a footballer switching from walking to suddenly running very quickly. In response, Ghaffari says he and his colleagues have published peer-reviewed papers , external on the accuracy of Epicore Biosystems' gadgets. He acknowledges that analysing sweat loss over short intervals up to 20 minutes long "can be challenging" but says his company's products appear effective for 30-minute, or longer, workouts. Perhaps the most common hydration-focused products available are the smart water bottles that remind you to take a sip throughout the day. "We try to make it fun," says Cem Bakiş, head of business development at WaterH, which has a glowing ring that blinks in order to prompt its owner to take a drink. "You can add friends, you can earn points." Some smart water bottles work by estimating the weight of liquid in them, and how that changes over time as the drink inside is consumed. But WaterH takes a different approach. …