Fitbit Flex Wireless Activity + Sleep Wristband, black. Tracks steps, distance, calories burned and active minutes Monitor how long and well you sleep Wakes you (and not your partner) with a silent wake alarm LED lights show how your day is stacking up against your goal Slim, comfortable and easy to wear (sold with both large and small wristbands included with an interchangeable clasp) Sync stats wirelessly and automatically to your computer and over 150 leading smartphones