A fitness tracker is a wearable device, usually in the form of a wristwatch, that tracks various metrics related to health and exercise. Most fitness trackers can monitor the daily step count, calories burned, miles walked, and heart rate of a user. Fitness trackers store information on their company's website and app by connecting to a compatible smartphone via Bluetooth. Users may visit either to view more accurate representations of the data collected by the device. A popular example of a fitness tracker is the Fitbit Flex, as shown in the picture.