How does this has been the cause of much schoolyard controversy but since the ring changes color because of thermo-reactive liquid crystal we have to assume it change because of fluctuation in temperature.. all that aside as your mood changes so does your body temperature. This ring picks up on that temperature change and the ring changes color along with your mood! Awesome! Great decoration for your fingers perfect for the men or the ladies. The best choice as the gift for your family friend boy friend or girlfriend. - Change the color automatically with different temperature - Comes with 5 different size (20.5mm/20.2mm/19.8mm/19.4mm/19mm) - Great and fancy Gift for friends