Early fitness trackers, such as pedometers, were primarily designed to count the number of steps taken by an individual.

The combination of the smartphone, the internet of things (IoT), and the miniaturization of sensors enabled the development of more sophisticated fitness trackers.

Optical heart rate sensors use light to measure heart rate by detecting changes in blood volume in the wrist.

Accelerometers measure movement, which can be used to track sleep patterns by detecting changes in body position and activity levels.

GPS tracking allows fitness trackers to map outdoor activities, such as running, cycling, and hiking, by recording the location data.

Fitbit was among the first fitness tracker brands to introduce advanced features like heart rate monitoring and sleep tracking.

Activity tracking in fitness trackers is primarily used to estimate the number of calories burned during various activities.

Photoplethysmography (PPG) is a technology used in fitness trackers to measure blood pressure by detecting changes in blood volume in the wrist.

Altimeter in fitness trackers is used to measure elevation gain during activities like hiking or climbing.

Garmin is known for its advanced GPS tracking capabilities and outdoor sports features in its fitness trackers.

Barometer in fitness trackers is used to measure air pressure, which can be useful for tracking elevation changes during activities like hiking or climbing.

Apple was among the first fitness tracker brands to introduce features like guided workouts and personalized coaching in its fitness trackers.

Gyroscope in fitness trackers is used to detect orientation and movement, which can be useful for tracking activities like running, cycling, and swimming.

Polar is known for its focus on professional athletes and advanced training metrics in its fitness trackers.

Magnetometer in fitness trackers is used to detect magnetic fields, which can be useful for tracking direction and orientation during activities like hiking or running.