Can a Health or Sleep Tracker Inform If You’re Sick?


It was early in the pandemic when my sleep tracker first panicked me. I tested SleepScore, Wirecutter’s choice for best sleep tracking app, and I found that my breathing was pretty normal, despite most of my data from the previous night (how much time I was in light, deep, and REM sleep spent) were pretty normal rate was twice as fast as usual. A quick Google search confirmed what I already knew – fast breathing could be the symptom of a respiratory disease. My mind jumped to the immediate conclusion, “Oh my god, I have the coronavirus.”

(Spoiler alert: I haven’t.)

It wouldn’t be the first time someone has visited a sleep tracker for disease detection. Sleep trackers are used to assess the quality of your sleep by typically measuring how long you sleep and how much time you spend in each phase of sleep. However, many sleep trackers – especially portable sleep and fitness trackers – collect a lot more data, including your nightly heart rate, heart rate variability (HRV), body temperature and breathing rate, and how long you sleep. Researchers have examined this plethora of data to see if they can identify the (often subtle) changes in people’s baselines that could predict the onset of infections like COVID-19, particularly asymptomatic or pre-symptomatic cases.

Sleep better

Sign up for our five-day email challenge to learn how small changes to your bedroom and mindset can optimize your sleep.


You can unsubscribe at any time

Since 2014, Michael Snyder, PhD, a professor of genetics at Stanford University who has founded and consulted a variety of precision medicine companies, has explored the potential of wearable sleep and fitness trackers (including Oura Ring, Fitbit trackers, and Apple Watch) for the detection of diseases, mostly based on heart rate data. He was even lucky enough to use the methods on himself and use a smartwatch to identify his own Lyme disease: “Basically, my heart rate increased and my blood oxygen decreased before I was symptomatic,” he says.

Since the pandemic began, Snyder and his team have been conducting their research to detect COVID-19. Recently, the team released results showing that by analyzing data collected from popular wearable sleep and fitness trackers, COVID-19 cases (on average) four days before symptoms started and seven days before diagnosis could be recognized. COVID-19 wasn’t the only focus of the study – influenza and other respiratory diseases were also detected two days before symptoms appeared.

Out of 50 Oura Ring wearers who contracted COVID-19, 38 had an elevated temperature that was recorded by their tracker before symptoms they could detect themselves appeared.

Last year I tested the Oura Ring, a wedding ring-like device that measures your heart rate, heart rate variability, breathing rate, and body temperature while you sleep. West Virginia University’s Rockefeller Neuroscience Institute (RNI) recently conducted a study specifically on the ring’s ability to track COVID-19. When you’re sick, your heart rate and breathing rate are likely to increase, and your heart rate variability is likely to decrease. Using an app, an AI model, and data from the Oura ring, RNI said, cases of COVID-19 were predicted with an accuracy of over 90% three days before symptoms appeared (the study was not peer-reviewed).

Meanwhile, researchers at the University of California at San Francisco have used the skin temperature monitoring features of the Oura ring to detect fever early on (this study was funded by Oura Health and some of the researchers are affiliated with the company). In their first peer-reviewed study of 50 Oura ring wearers who contracted COVID-19, 38 of them had an elevated temperature, which was detected by continuous monitoring of their tracker, before symptoms that they detect themselves appeared could. Based on the Oura Ring’s initial promise to detect asymptomatic and pre-symptomatic COVID-19, the NBA offered rings to players who participated in the “Bubble” in Orlando, Florida last summer.

However, there is a downside to all of the potential of these devices. A small 2020 study by the University of Copenhagen in 27 patients with chronic heart disease found that using fitness trackers can increase anxiety, especially when wearers fail to meet their fitness goals or have alarming health data (something I look to mine Respiratory rate could identify horror). The scientists concluded that for these devices to be most useful, people would need the guidance of health professionals to correctly interpret the data.

And then there is the possibility that the device will take an incorrect measurement due to some defect or user error. That may have happened to my elevated reading, which turned out to be not an early sign of infection. My early morning health shock was likely the result of testing multiple sonar sleep trackers at the same time, an occupational hazard at Wirecutter. (With twice as many sonar waves reflecting off my chest, it makes sense that I may not have read.)

After many months of testing these devices, I am ambivalent about their usefulness for this type of predictive health monitoring. At a time when I was already very vigilant about my health, struggling with so much data from the devices and apps became more unsettling than comforting. Obviously, reliable and accessible tests, safety precautions like masking and vaccination are better ways to get out of the current pandemic. For now, I will continue to use sleep trackers to learn more about my sleep patterns and (maybe) get a heads up if I have a cold.

It’s sleep week at Wirecutter! Read about the best sleep week deals on our expert-recommended mattresses, linens and more for your bedroom.

further reading