Fitness Tracker

A fitness tracker is a wrist-worn wearable device that continuously monitors physical activity — steps, distance, calories, heart rate, and sleep — syncing data to a smartphone app for analysis and goal tracking. Smaller and cheaper than a smartwatch, fitness trackers prioritise health data and battery life over app functionality and display quality. Fitbit — acquired by Google in 2021 — pioneered the consumer category, while Xiaomi’s Mi Band series dominates the budget segment globally.

A fitness tracker is a slim wristband typically 0.5 to 0.8 inches wide and 0.3 to 0.5 inches thick. The band — silicone, elastomer, or woven fabric — wraps the wrist and fastens with a traditional pin buckle or magnetic clasp. A small display module is integrated into the band or sits in a separate capsule that slots into the band.

The display is small — 0.5 to 1.4 inches diagonally — OLED or LCD, monochrome or colour. It shows steps, time, heart rate, and notification alerts in a simple scrolling interface. Many budget trackers have no display at all — only LED indicator lights showing activity levels. Battery life ranges from five to thirty days depending on display and GPS features, far exceeding the one to two day life of a comparable smartwatch.

A heart rate sensor on the band’s inner face sits against the wrist skin — a small optical sensor cluster with green LEDs. Premium models add blood oxygen (SpO2) sensors. GPS is absent on most fitness trackers — they rely on the connected smartphone’s GPS for route tracking — though some premium models include onboard GPS.

Brand identification: Fitbit Charge and Inspire bands use a characteristic narrow silicone band with a small rectangular screen module. Xiaomi Mi Band uses a pill-shaped capsule that detaches from the band. Garmin Vivosmart uses a slightly wider band with a more pronounced display module.

A fitness tracker counts steps using an accelerometer, estimates distance and calories burned from step data and user profile, monitors heart rate continuously, tracks sleep stages and duration, and syncs all data to a smartphone app. The app provides daily, weekly, and long-term trend analysis, goal setting, and comparisons against personal bests and community averages. Notification alerts from the paired smartphone are displayed on the tracker screen as a secondary function.

1. A three-axis accelerometer detects wrist movement and uses algorithms to distinguish walking, running, and other activity patterns from random movement — counting steps by identifying the characteristic acceleration signature of each footfall.
2. The optical heart rate sensor uses green LED light and a photodiode to measure the variation in blood volume in the wrist capillaries with each heartbeat — the same principle as a hospital pulse oximeter but implemented for continuous wrist monitoring.
3. Sleep tracking uses the accelerometer to detect periods of low movement and combines this with heart rate data to estimate sleep stages — light, deep, and REM — through proprietary algorithms.
4. Bluetooth Low Energy transmits accumulated data to the paired smartphone app periodically throughout the day, minimising battery consumption compared to continuous transmission.
5. The companion app applies the raw sensor data through calibrated algorithms to produce the step counts, calorie estimates, and sleep scores presented to the user.

Pedometers — mechanical step counters worn on the hip — have been commercially available since the 1960s and were widely used in Japan’s 10,000 steps per day health campaigns from the 1960s onward. The modern wrist-worn fitness tracker emerged from the convergence of miniaturised accelerometers, Bluetooth Low Energy, and smartphone app ecosystems in the early 2010s.

Fitbit, founded in San Francisco in 2007 by James Park and Eric Friedman, launched its first clip-on tracker in 2009 — a small device worn on the clothing rather than the wrist. The Fitbit Ultra in 2011 and Fitbit Flex in 2013 — the first wristband model — established the wrist tracker format. Fitbit went public in 2015 at a $4.1 billion valuation, reflecting the extraordinary consumer traction the category had achieved.

Jawbone and Nike FuelBand were early competitors that did not survive — Jawbone ceased operations in 2017 and Nike exited the hardware wearables market in 2014. Xiaomi entered the market in 2014 with the Mi Band at $13 — a fraction of Fitbit’s pricing — and rapidly became the world’s best-selling fitness tracker by unit volume.

Google acquired Fitbit in January 2021 for $2.1 billion. The acquisition was controversial due to the health data implications of a major technology company owning one of the world’s largest personal health datasets — covering over 29 million active users. The fitness tracker category has been partly absorbed by the expanding smartwatch market but retains distinct appeal for users prioritising battery life, simplicity, and price.

• Electronics retailers and sports stores for current production
• Online via Amazon — the dominant sales channel
• Pharmacy and health-focused retailers for Fitbit and health-positioned brands
• Secondhand via eBay and marketplace apps — battery condition is the key concern
• Thrift stores for older Fitbit models at low prices

Smartwatch: A full computing platform on the wrist with app store, larger display, and broader functionality beyond health tracking. Distinguished by its larger square or round case, colour touchscreen, and ability to run third-party applications. The line between premium fitness tracker and entry-level smartwatch is blurred on devices like the Fitbit Versa and Xiaomi Smart Band Pro.

Medical-grade wearable: Clinical monitoring devices — continuous glucose monitors, ECG patches, hospital telemetry bands — share wrist or body placement with fitness trackers but are distinguished by their medical device certification, prescription requirement in some markets, and clinical-grade sensor accuracy.

Smart bracelet or jewellery tracker: Fashion-forward devices that embed minimal activity tracking in jewellery forms — rings, bracelets, necklaces. Distinguished by their non-functional-appearance design that prioritises aesthetics over sensor capability.

Fitness trackers depreciate quickly and have limited secondhand appeal due to battery degradation and rapid feature obsolescence.

• Xiaomi Mi Band 8 or 9 new: $30—$50
• Fitbit Charge 6 new: $140—$160
• Fitbit Inspire 3 new: $80—$100
• Garmin Vivosmart 5 new: $130—$150
• Used Fitbit models two generations old: $15—$40
• Original Fitbit Flex (2013) as curiosity: $5—$15

Battery replacement is complex on sealed wristband designs and typically not practical — a tracker with degraded battery life has limited remaining value regardless of external condition.

Smartwatches increasingly include all fitness tracker functions while adding display and app functionality, eroding the distinct fitness tracker market at the premium end. Smart rings — Oura, Samsung Galaxy Ring — provide health monitoring without any wrist display for users who prefer a minimal form factor. Smartphone-based step counting via the phone’s built-in accelerometer is free and effective for basic activity tracking without a dedicated device. The fitness tracker market is under competitive pressure from both directions — smartwatches from above and smartphone apps from below — but the combination of low price, long battery life, and simplicity maintains a distinct consumer segment.

Looking for one? Where to buy a Fitness Tracker →

Looking for one? Where to buy a Fitness Tracker →

• Slim wristband 0.5 to 0.8 inches wide in silicone, elastomer, or woven fabric
• Small OLED or LCD display 0.5 to 1.4 inches — or LED indicators only on budget models
• Optical heart rate sensor on inner band face against wrist skin
• Pin buckle or magnetic clasp fastening
• Battery life 5 to 30 days — significantly longer than a smartwatch
• Bluetooth sync to companion smartphone app
• Magnetic or pogo-pin charging connector on the tracker capsule
• Brand: Fitbit, Xiaomi Mi Band, Garmin Vivosmart, or Huawei Band