While it may look like a simple piece of foliage, the Leaf thermometer is far from it. Designed by Hideyuki Kumagai, the Leaf thermometer is a leaf-shaped temperature measuring device that will actually change color according to different degrees of hotness or coldness. When the temperature is warm and about 20 to 25°C, the Leaf will stay its natural green hue. As it gets hotter, it will turn a bright yellow, but if it gets colder, it will turn brown.
The Leaf thermometer is made from paper and is currently available at Japan Trend Shop. You can buy it in a pack of five large leaves or a pack of eight small ones, which the site says is great for scattering around the office or home to "tell you the temperature in the most innovative way possible."