In May 2013, Fitbit released the Fitbit Flex, which is a device that one wears on the wrist. It tracks movement 24 hours a day, including sleep patterns. It has a simple display of 5 LED lights which indicate the number of steps taken in a day, and it vibrates to indicate that your goal has been reached. The lights also indicate battery level.

The Fitbit Flex has almost all the same sync functions as the Fitbit One and Zip. Compared to the One, the altimeter has been removed. The Flex is also the first water-resistant tracker; it can be worn while showering and swimming. The Fitbit flex includes a specialized USB charger; the battery lasts 5-7 days, and it takes 1-2 hours to charge.