There's nothing like thick, juicy slices of watermelon in the summertime. But how do you know when it's ripe?

Thanks to University of Arizona agricultural and biosystems professor Mark Riley, we won't have to guess. He says that "consumers often buy peaches, pears and melons they can't eat because they're under-ripe or overripe." Consequently, he decided to develop RediRipe stickers that can detect ethylene gas, which is said to be released by fruit or vegetables as they ripen.

The RediRipe sticker will turn from white to blue to indicate that it is ripe. However, it takes about 24 to 48 hours for the stickers to change color because a fruit can't ripen instantenously.

However, Riley has walked into some walls while developing the stickers. "The stickers do not change color to reflect an overripe or rotten piece of fruit. Also, not all fruit produces enough ethylene to be detected by the sticker."

Currently, the stickers have been tested at an apple orchard and will expand to other field tests this fall. Each sticker will cost growers and grocery stores about a penny.

[All quotes from USAToday.com]