Fitness trackers do a lot more than count steps. Here at PCMag, we take many factors into account in our reviews of these devices, including accuracy, battery life, ease of setup and use, features, specs, and style. This helps us determine the strongest options at every price level, as well as which models deserve a spot in our roundup of the best fitness trackers. (Many smartwatches have fitness- and health-focused features too, so we use much of the same criteria to test their wellness prowess.) For a better understanding of how and why we perform our tests, this is what we look for when making an evaluation.
Fitness Tracker Design and Comfort
It doesn’t matter how useful a fitness tracker is if it’s just going to collect dust at the bottom of a dresser drawer, so make sure to get a tracker you want to wear. Everyone has different tastes, so we’re not looking for a single design that makes everyone happy. We are, however, looking for versatility. Trackers with interchangeable straps and lots of available accessory bands score extra points because you can dress them up for formal events or dress them down for the gym.
Comfort matters, too. Aside from occasional breaks to give your skin a chance to breathe, you should wear your tracker 24/7 for the most accurate and consistent activity and sleep metrics. To evaluate their comfort level, we wear trackers day and night for about a week (or longer if time permits). We wear them during workouts, in the shower if they’re water resistant, while running errands, and to bed if they track sleep.
It can be challenging to wear a tracker to bed if you’re not used to it, but a slim, lightweight design and features like Sleep Mode, which typically dims the display and disables vibrations, can combat wearable-induced insomnia.
How Long Do Fitness Trackers Last?
After reaching a full charge, we wear each tracker until the battery dies and note how long it lasted. If text, call, and app notifications are available, we turn them on. If the tracker has an always-on display, we enable it. Once the battery drains, we time how long it takes to recharge the tracker back to full.
Many factors impact battery life, and we consider all of them in testing. While some trackers won’t last more than a day or two, others can go weeks or more (in which case we usually quote the manufacturer’s battery estimate). A general rule of thumb is that the more advanced the device, the shorter it lasts. Color touch screens, continuous heart rate monitoring, and built-in GPS can quickly drain the battery.
For example, while three or four days on a single charge might not seem impressive, it is if the tracker has all of those advanced features. Most modern smartwatches, for instance, require you to charge them every day. But many also boast fast-charging capabilities, allowing them to juice quickly.
Sensors and Smartwatch Features
In addition to the sensors mentioned above, we look for several others when evaluating new trackers. The most basic models include a three-axis accelerometer that measures steps and distance traveled. To measure heart rate, manufacturers generally opt for an optical sensor (the green flashing light you usually see on the underside of the display). Some trackers also include barometers and altimeters to measure elevation.
The more sensors you have, the less likely you are to need your phone nearby. For example, models with a built-in GPS can measure your pace and distance during outdoor workouts without the help of your smartphone.
Many of the latest trackers go beyond just keeping tabs on your activity and workouts. COVID-19 has spurred a new generation of wearables with advanced health-monitoring capabilities, including the ability to measure your blood oxygen saturation (SpO2 or Pulse Ox) level, body temperature deviations from your baseline, respiration rate (the number of breaths you take per minute, and heart rate variability (a measure of your nervous system activity and an indicator of stress level).
For connectivity, Bluetooth is pretty much a given, but you might find models with a cellular modem. Some smartwatch-tracker hybrids even come with the option to store and stream music directly from the device itself, which means you can leave your phone at home.
Testing Fitness Tracker Accuracy
When it comes to measuring accuracy, we first examine whether a fitness tracker’s heart rate, sleep, and other health metrics are realistic and consistent. Extreme inaccuracies are rare, but easy to identify. For instance, based on my extensive fitness tracker testing, I already know my maximum heart rate is around 189bpm. If a fitness tracker I’m testing tells me that my heart rate is 200bpm or above, chances are it’s wrong.
Next, we compare a fitness tracker’s metrics to that of a control device, the accuracy of which we have already verified, such as the Polar OH1 heart rate monitor or the Apple Watch Series 7 smartwatch. For exercise data, we work out (usually indoors on a smart home gym machine we’re also evaluating) while wearing both the fitness tracker we’re testing and a control device. During the workout, we perform numerous spot checks to see how the numbers correspond. After the workout, we compare the average and maximum heart rate readings, plus calorie burn estimates for the session.
If a tracker has an integrated GPS, we take it for a run outside. We wear a control device on the other wrist to compare their pace and distance results. To verify SpO2 accuracy, we take at least three to five readings on both the fitness tracker we are evaluating and our control device, alternating between the two. Then, we calculate the average for each and compare the results.
Just like how you are likely to get 10 slightly different results if you step on 10 different smart scales, we expect minor variances in the metrics from one fitness tracker to the next, especially when it comes to calorie burn estimates. That said, their metrics should be in the same ballpark. For heart rate readings, we find an acceptable margin of error to be 5 to 10bpm. SpO2 readings should be within 1% to 2% of the control device. For cases in which we get abnormal results, we perform additional tests, sometimes with a different control device.
For sleep data, we generally compare a fitness tracker’s overnight metrics to several control devices like a Google Nest Hub smart display and Sleep Number 360 i8 smart bed, both of which we use on a regular basis to track sleeping.
Beyond the Wrist
The test methods we outlined above primarily apply to wrist-based trackers. But by and large, the process remains unchanged for fitness trackers with other designs such as the Oura Ring.
Ultimately, the best fitness tracker for you comes down to your budget, health goals, and activity levels. To learn more, check out our roundup of the best fitness trackers overall, as well as our top picks for runners and swimmers.
