Lightweight & Portable: Small size, the weight of 1pc keychain light is only 8g, easy to carry around. Has a 1" link chain. Easy to Use: Two modes for turning on the UV light, ON/OFF switch or squeeze button. Built-in Button Batteries: Powered by 2 * CR2016 lithium batteries, which was installed in the product. UV Checking: UV light can be used for detecting currency, passports, etc. It also can be used to test whether baby's diapers, clothes and other baby products contain fluorescent agents.