The black Fitbit Flex Wireless Activity and Sleep Tracker Wristband is a water resistant band that you wear on your wrist to track vital daily stats. It tracks your steps taken, distance, and calories burned. It also measures your sleep quality and has a silent alarm that vibrates to wake you up - rather than beeping which could wake others. The Flex features Bluetooth 4.0, so it syncs wirelessly with your devices automatically whenever it is within 20' of them. Both a small and large wristband are included to ensure a comfortable fit, as well as a wireless sync dongle and charging cable.