Figuring out how long you can stay in the sun before getting a vicious sunburn can be tricky, especially if you have pale skin. These wristbands eliminate most of the guesswork by measuring the amount of UV exposure you've had, and letting you know when to cover up.
The bands were developed by a team at Strathclyde University in Scotland, and work through an acid-release agent which picks up ultraviolet light, and a dye which responds to pH levels in the indicator. Once the UV exposure reaches a predetermined level, the bands change rapidly from yellow to pink.
Because people with different types of complexion have differing reactions to UV exposure, the bands will come in several sensitivity levels. Designed to be a one shot disposable item, Swedish manufacturer Intellego Technologies says the bands will be pretty cheap at less than a quarter each.
Just try not to fall asleep on top of the arm with the band.