In recent year, wearable technology is on the rise in personal and business use. Wearable devices, such as smart watches, smart bands, activity trackers, smart glasses, or the like, become more and more popular. Most of the wearable devices have the capability of computing and are able to be connected in wired or wireless way with mobile devices such as smart phone or tablet. Wearable devices can be used to monitor and track fitness-related metrics of human, such as distance walked or run, calorie consumption, and in some cases heartbeat and quality of sleep.
Photochromism is the reversible transformation of a chemical species between two forms by the absorption of electromagnetic radiation, where the two forms have different absorption spectra. Thermochromism is the property of substances to change color due to a change in temperature. Nowadays, photochromic/thermochromic materials have been incorporated into electronic devices for various uses.