The Doctor on Your Wrist

“The unexamined life is not worth living.” So said Socrates, and I’m trying to live up to the philosopher’s credo–in a 21st century way. On my wrist I wear a Jawbone UP24, a rubber bracelet that tracks my steps and calories burned over the course of the day. To make sure I don’t exceed the calories burned with calories consumed, I track my diet with the iPhone app MyFitnessPal, which syncs up with my Jawbone data. The Jawbone bracelet uses a motion sensor to track my sleep time, and the Jawbone app uses algorithms to calculate the hours I spend in light sleep and deep sleep over the course of the night. While I trained for the New York City Marathon, I tracked my runs with the iPhone app RunKeeper, which allowed me to see myself very slowly getting somewhat faster.

That kind of numeric detail probably isn’t what Socrates had in mind, but more and more of us are engaging in some form of digital self-examination. Research firm ABI estimates that 42 million wearable fitness and health devices will be shipped in 2014, up from 32 million in 2013. The movement even has a name–the quantified self–and its geekiest adherents go far beyond what I could bring myself to try. They carry digital cameras around their necks that capture a constant stream of visual memories and wear heart monitors and blood-pressure sensors up and down their torsos. They treat their bodies as guinea pigs and gather in meet-ups and conferences to swap stories–backed by data, of course–about the best ways to lose weight, work more efficiently and get smarter.

Hardcore disciples and those who, like me, just try to remember to wear a wearable share the same hope: that through collecting ever more information about our bodies and our behavior, we can find a better route to self-improvement. Doctors and researchers see something else in the movement too–a revolution that could change everything from how they care for recovering surgery patients to the way they administer certain medications. Tracking devices may eventually even upend how much you pay in health-insurance premiums. And they may ultimately change the way we relate to our own health.

But before you can really know thyself, you need to know thy data.

The logging of personal information has a rich history. Benjamin Franklin kept a meticulous chart book noting his progress on 13 virtues, and dieters in programs like Weight Watchers have long counted calories. But as anyone who has ever tried to keep a regular journal knows, recording it all on paper requires a commitment few of us can keep up for long. Digital self- tracking devices–often connected to the Internet through our smartphones–take the effort out of recording and compiling. You get better, more regular data, and it’s harder for you to fudge it to make yourself feel better. That also means the information is easily shareable with doctors.

To that end, hospitals are already a step ahead. The Cleveland Clinic has asked its employees and their family members–more than 50,000 people in all–to use the Pebble, an activity tracker, in the hope that it will encourage them to move more. So far, more than 18,000 people have met the goal of 100,000 steps a month or 600 activity minutes a month for six months. (That’s roughly 20 minutes a day.) There’s an added benefit: employees and family members who use the Pebble are eligible for a lower health-insurance premium.

Using Jawbone’s sleep app, I’ve seen how data analytics can make a daily difference. With Jawbone, I’ve come to understand that certain factors–stress, alcohol and caffeine–can influence how restful my sleep really is. The device’s accelerometer detects whether I’m moving and, roughly, whether I’m awake or in a light or deep sleep. The next morning, the app displays a graphic summary of my night. Over the weeks, I’ve been able to track how my sleep time has waxed and waned and how often I meet the 7½ hours I’ve set as a nightly goal.

I’ve found that I get the most sleep on weekends–unsurprisingly–but I’ve also noticed that my sleep tends to decline as the workweek drags on, perhaps because stress levels rise with each day. Just keeping track of how much time I’m actually spending awake has encouraged me to get to bed at a relatively reasonable hour and overcome the temptation to watch one more episode of Damages on Netflix.

Health professionals are finding that simply tracking an activity can encourage people to do more of it. In Minnesota, for instance, the Mayo Clinic experimented by using activity trackers to help with postsurgery care. In 2013 the hospital equipped nearly 150 heart-surgery patients over the age of 50 with Fitbit activity trackers on their first day of recovery. The reason: older patients tend to lose mobility in the wake of major surgery, which can slow recovery. The researchers found that patients who took the most steps every day–data tracked by their Fitbits–were significantly more likely to leave the hospital earlier than those who were less active, and they were also more likely to return home rather than to a nursing facility. Doctors knew that only because they were keeping track of a data point they had never bothered to record before.

The most valuable analysis comes when researchers are able to draw on a wide pool of data. And the growing ubiquity of fitness and activity trackers has made that pool into an ocean. It’s also caused some worries–the IT security firm Symantec reported in June that fitness trackers were often vulnerable to hacking. But the data keep flowing. Jawbone users around the world have recorded more than 130 million nights of sleep–which, as the company’s vice president of data, Monica Rogati, notes, technically makes it the biggest sleep study in the world–as well as more than 1.6 trillion steps and 180 million items of food. “You take all that data, and you can see interesting patterns emerge,” she says.

For example, Rogati knows that in the U.S., people in Southern states move the least. She knows that New Yorkers have a huge swing in sleep time between the weekdays and the weekends, whereas people in Orlando–a city well stocked with retirees–get similar amounts of sleep throughout the week. During the 2013 Super Bowl, which went down to the wire, she saw sleep numbers drop nationwide–but not during the 2014 Super Bowl, a blowout that many people tuned out early in the night. She can actually see the passage of Ramadan, a month when observant Muslims fast throughout the day, in a Middle Eastern city like Dubai. “People become less active during the day and sleep more, essentially become nocturnal,” she says. “The data tell you something about the signature of the city.”

All this information will matter only if we can learn something more valuable than the fact that a boring Super Bowl leads to an earlier bedtime. In a growing trend, Jawbone uses its data to produce personalized nudges designed to encourage users to sleep more, be more active and eat better. That analysis has also helped produce the smart-alarm function for the UP wristband. The Jawbone smart alarm tracks which sleep stage you’re in near your preferred waking time and buzzes your wrist when you’re in a light stage–hopefully nudging you out of bed at the right time biologically. “Sleep is as important as fitness and nutrition,” says Jason Donahue, product manager for data and insights at Jawbone UP. “By tracking it, you can give it the attention it deserves.”

Activity trackers are far from perfect. Some are bulky and unfashionable, and all suffer from accuracy problems. A 2014 study by researchers at Iowa State University looked at top fitness trackers and found that on average, they were 10% to 15% off in calculating the calorie burn from exercise and daily activity. But with each generation, the devices are getting smaller and more precise. The highly anticipated Apple Watch is supposed to be able to detect which activity you’re doing as you do it, along with your heart rate, which helps improve calorie-burn calculations.

Jawbone’s newest device, the UP3, will track heart rate using bioimpedance sensors, which measure the resistance of body tissue to a tiny electric current generated by the bracelet. In the future, the company believes the sensors will be able to detect skin temperature, respiration, hydration and more. That means greater quantities of finer data to feed into Jawbone’s algorithms, which in turn improves the advice the company dispenses as it tries to get you to eat better, sleep longer and be more active. “No one else has been able to get this amount of data on something small enough to wear on your wrist 24/7,” says Travis Bogard, Jawbone’s vice president of product management and strategy.

The new UP will enter an already crowded fitness-tracker market. Microsoft just released its first tracker–the Microsoft Band, which promises to track heart rate and an array of other data points. The first batch of smart watches using Google’s Android Wear operating system provides fitness functions like tracking runs or bike rides. And increasingly, most smartphones from the likes of Apple and Samsung have pedometers built right in.

That puts extra pressure on a company like Jawbone that produces dedicated activity trackers. There’s a lot riding on the success of the UP3, which Bogard and other executives at Jawbone were already using when I visited the company’s San Francisco headquarters in early October. But the excitement at Jawbone was generated less by the devices than by the data they produce–and the unexpected lessons Rogati’s team of data scientists could produce from all those bits and bytes. One wall of Jawbone’s open-plan office was covered with data stories generated by tracking millions of users, ranging from how the World Cup affected sleep patterns to a list of the most popular foods by time of day. (Beer: very popular after midnight, not so much before noon.)

Bogard believes that the future of self-tracking isn’t about the tracker; it’s about the self and the data it produces. “Our belief is that the tech itself should disappear,” he says. “The technology becomes an enabler to help us become more human.”

Once tracking has become ubiquitous, it could produce a health revolution. Right now, doctors have to wait for us to feel bad enough to bring our bodies into the shop; until we do, they’re in the dark. Data tracking could make it a lot easier for someone who is, for example, trying to manage a weight problem–especially if the data could be automatically uploaded to a doctor’s office. No more lying about how much you exercise or snack.

And personal data can mean personalized health care. The real winner may be not the company that makes the best device but the one that can produce a meaningful signal out of the noise of personal data. “No one thing works for everyone,” says Andrew Rosenthal, the group manager for wellness and platform at Jawbone. “We can help steer people toward the health solutions that work best for them.”

But as someone who began practicing self-quantifying for this story and has since become all but addicted to it, I can say there’s a personal side to this movement as well. So much of our health today feels out of our hands, the province of medical professionals. Self-quantifying has allowed me to take control of my health, to track and tweak my habits, to make myself a better person. Today I feel like a test group of one–but I’m in charge of the experiment, and I benefit from the results. You can count on it.

–WITH REPORTING BY ALEXANDRA SIFFERLIN / NEW YORK