UV SunSense wristbands make it easy to monitor sun exposure with a simple color-changing gauge alerting when it's time to reapply sunscreen or to get out of the sun all together.
The band is calibrated to work with sunscreen of SPF 15 or higher, and you have to apply sunscreen over exposed skin as well as on the band. After exposure to the sun, the band turns purple to indicate it has been activated. There's a caveat: bands shouldn't be reused as they'll only start monitoring UV rays from when you last took it out of the sunlight.
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