Do you know how to pick a ripe watermelon? Our mom hits it like a drum — if it sounds deep and empty, then it’s good. …or not. Sometimes, definitely not good. So now there are sensors that are stuck on the skin of the food directly to tell how far along its ripeness (or foulness) the fruit is! Check out the article from Gizmodo: Edible Sensors Let You Know If Your Food Is Spoiled.