Sunshine on a biting fall day can feel blissful. But too much time spent basking in the sun’s ultraviolet rays can lead to sunburn and increase the risk of developing skin cancer, cataracts and wrinkles. Now, researchers have made a cheap, wearable device that keeps tabs on UV exposure. The new tech could mean soaking up the sun without overdosing on radiation.

Vipul Bansal, an applied chemist and nanobiotechnologist at the Royal Melbourne Institute of Technology in Australia, wanted to m