The Fitbit Flex Wireless Activity + Sleep Wristband in black is a brand new, unisex activity tracker from Fitbit. It is designed for indoor and outdoor use, providing measurements for calories and distance in both decimal and imperial systems. The wristband features a wireless design, up to 5 days of battery life, and operates on iOS systems. Made of plastic, it is suitable for those looking to track their fitness progress, especially in running and jogging activities.