Wearable Insights

Fitness and activity trackers: sensors, battery, and what the app charges for

A fitness tracker is a smartwatch with the watch taken out: a small screen or none, a week or two of battery, and the sensors that count steps, heart rate and sleep. Its specification sheet is short, and the most expensive line on it is often the one about the app.

What the category is

Screen trackers: slim bands with a small colour display — Fitbit Charge and Inspire, Xiaomi Smart Band, Samsung Galaxy Fit, Amazfit Band — that show the time, notifications and a workout. Screenless trackers such as Whoop, worn for recovery data and read on the phone. Budget bands from small brands with their own app, sold as “smart bracelets”. A tracker with a large screen and calling is a smartwatch.

How to read the spec sheet

Sensors: optical heart rate (continuous or on demand), SpO2, skin temperature, and on the better bands an ECG. The sheet lists them; it does not rate them.

Battery in days: 7 to 14 is the category’s point. A band that quotes 5 days with always-on is a small smartwatch.

GPS: built in (rare on a band, and it halves the battery), connected through the phone (common), or none. A runner who wants a route without a phone needs the first.

Water rating: 5 ATM for swimming, and whether swim tracking is a mode.

Display: size, AMOLED or not, always-on or not, and whether it shows notifications or only counts.

Compatibility and the app: iOS and Android, the app’s name, and — the line that matters — what the app charges for. Fitbit’s detailed sleep and readiness are behind Premium; Whoop is a subscription with the band included. The manufacturer’s own page says so and a review quotes it.

Strap: width, material, and whether it is swappable. A tracker whose strap is the body is a tracker you replace when the strap breaks.

Who it suits

Anyone who wants steps, heart rate, sleep and a fortnight of battery without a second screen. A swimmer wants 5 ATM and a swim mode; a runner without a phone wants built-in GPS; a data person wants a screenless band and accepts the fee.

Who should skip it

Anyone who wants to answer a call or pay from the wrist, which is a smartwatch. Anyone who mainly wants sleep and recovery and nothing on the wrist in the day, which is a ring.

Where to start

Six of the 102 fitness & activity trackers wearables reviewed on this site, one per model, across manufacturers. Every review is written from the manufacturer’s published specifications — how, and what that leaves out.

All 102 fitness & activity trackers wearable reviews

Newest first. Consumables, accessories and parts that were once filed here are excluded.