The sticker, called RediRipe, detects a chemical called ethylene gas, which is released by fruit or vegetables as the ripen. According to Mark Riley, an assistant professor at the University of Arizona, the sticker will turn from white to blue as the fruit ripens.
Riley says it takes 24 to 48 hours to determine how fast the fruit is ripening. But the stickers are not without own bugs. They have yet to change color to show when a fruit is rotten or simply overripe.