Do You Need a Wearable Device, or Just Your Smartphone?

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A major draw of the growing selection of wearable devices is their ability to track users’ physical activity unobtrusively and accurately. But what if a device you already carry in your pocket is just as accurate at tracking your activity and counting your steps? Would you still need to buy a wearable for basic fitness tracking?

A study published by the Journal of the American Medical Association, titled “Accuracy of Smartphone Applications and Wearable Devices for Tracking Physical Activity Data,” claims that smartphones are just as good — if not marginally better — at tracking physical activity as the most popular wearable devices. The researchers’ findings beg the question: If smartphones are accurate enough, will anyone other than serious enthusiasts need to buy another device to be more informed about their health and fitness?

To compare the accuracy of smartphone apps with popular wearable devices, researchers at the Perelman School of Medicine and the Center for Health Incentives and Behavioral Economics at the University of Pennsylvania recruited healthy adults aged 18 and older to walk on a treadmill at 3 miles per hour, twice each for 500 and 1,500 steps. An observer counted participants’ steps independently, using a tally counter. A sample of 10 apps and devices was selected from among the top sellers in the United States.

On the waistband, each participant wore the Digi-Walker SW-200 pedometer by Yamax, and Fitbit’s Zip and One clip-on trackers. On the wrist, each participant wore the Fitbit Flex, the Jawbone UP24, and the Nike FuelBand. In one pocket, each carried an iPhone 5s simultaneously running the Fitbit app, Withings Health Mate app, and ProtoGeo Moves app. In the other pocket, each carried the Samsung Galaxy S4 running the ProtoGeo Moves app. 552 step count observations were recorded from 14 participants in 56 trials.

The researchers found that many of the apps and wearable devices were accurate for tracking step counts. The data obtained by the smartphones was only “slightly different” from the observed step counts, but could be higher or lower than the actual number of steps. But the data from the wearable devices differed more, and one device reported step counts more than 20% lower than what was observed.

Apple Insider’s Sam Oliver reports that data collected from the iOS and Android apps had a range of -6.7% to 6.2% relative difference from the number of steps researchers observed the participants taking, while the data collected from the wearables had a range of -22.7% to -1.5%. Oliver also notes that the research shows that Nike’s FuelBand was sometimes “wildly off,” and Jawbone’s Up24 and Fitbit’s Flex showed the second- and third-largest deviations. Fitbit’s Zip and One, by contrast, were nearly perfect in their accuracy to the step counts observed by researchers.

As the study points out, adoption of wearable devices — even those like the pedometer, which has been widely available for years — is low, especially when compared to the high adoption of smartphones. The study’s authors note, “Our findings suggest that smartphone apps could prove to be a more widely accessible and affordable way of tracking health behaviors.” The study suggests that if you want to accurately count your steps or track your physical activity, you may be better off sticking with your iPhone than purchasing one of the wearables currently on the market.

The findings seem especially relevant to Apple, which will soon offer products in both categories investigated by the researchers. The iPhone 5s, iPhone 6, and iPhone 6 Plus feature M-series motion coprocessors that constantly measure the motion of the device, and share step data with the iOS Health app. Health and fitness-tracking abilities are also a major selling point of the upcoming Apple Watch, which will include an accelerometer for tracking steps and body movements.

But if the iPhone is already good at tracking your steps and daily activity, Apple will find it more challenging to sell the Apple Watch on the basis of fitness tracking. If smartphones are accurate enough, only those consumers who are serious about tracking their workouts and quantifying their fitness with more advanced metrics will need to buy another device. For them, Apple’s Health app and its ability to collect data from multiple apps and devices could prove an important selling point for the Apple Watch, regardless of whether the iPhone is just as accurate as a device that could be more easily worn during more intense workouts.

It’s also worth noting that the Apple Watch is still a device in search of a killer app, and fitness tracking is far from the only function that it’s designed to fulfill. Some, like Cult of Mac’s Luke Dormehl, think that fitness tracking will hardly register within the top 10 use cases for the new wearable. As Apple and the third-party developers creating apps for the Apple Watch figure out how best to leverage the platform, the general consumer could still be convinced that the Apple Watch is indispensable, even if the iPhone is just as accurate when it comes to counting steps.

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