Rather than trying to guess when you’ve had enough sun exposure, you may soon be able to simply check that sticker on your arm. Made with proprietary inks, the LogicInk UV stickers by San Francisco-based LogicInk will change color based on the sunlight.

They come in two designs, either two straight lines or two circles with one inside the other, and are waterproof and intended to be worn underneath sunscreen. One line will change color immediately upon stepping into the sun, becoming a shade anywhere between white and purple that signals the sun’s current intensity. The second line is divided into three segments, which slowly change color from purple to bright pink, one after the other, as they spend time in the sun. When all three are bright pink, it’s time to head inside.

LogicInk hopes to launch the stickers in the second quarter of 2018.