Your Smartwatch May Be Tracking Your Sleep Wrong

Not all wearables are equal when it comes to sleep tracking, researchers say. 

The most accurate way to measure sleep is in a laboratory using special equipment. But scientists recently published a study in the journal Sleep, which found that several devices, including one by Fitbit, nearly equaled professional monitoring devices. Another study published in Nature & Science of Sleep found that the Fitbit Ionic and the Oura Smart Ring got the highest marks for accuracy. Independent experts say they aren’t surprised by these findings. 

"Recent research has indicated that sleep trackers are only accurate 78% of the time when identifying sleep versus wakefulness as compared to higher accuracy offered by polysomnography tests," sleep researcher Wayne Leslie Ross, who was not involved in the studies, said in an email interview. "In addition, the accuracy of sleep trackers further drops to around 38% when estimating how long participants took to fall asleep."

Garmin Trails the Pack

The researchers who published the study in Sleep compared four wearable sleep-tracking devices (Fatigue Science Readiband, Fitbit Alta HR, Garmin Fenix 5S, Garmin Vivosmart 3) and three non-wearable sleep-tracking devices (EarlySense Live, ResMed S+, SleepScore Max) against lab equipment. All of the gadgets, except Garmin’s, performed at least as well as the professional equipment.

The Nature & Science of Sleep article claims that the Fitbit Ionic and the Oura Smart Ring were the most accurate of the devices tested, compared to professional sleep monitoring equipment. The Apple Watch Series 3 and Garmin Vivosmart 4 were among the wearables that performed the worst in the study. 

Analyzing How We Sleep

Sleep is critical to health, Chris Fernandez, CEO and co-founder of EnsoData, a company that uses AI to analyze health conditions, said in an email interview. 

"Humans spend between a third and a quarter of their lives asleep, yet only recently did we begin to study sleep’s profound impact on our overall health and happiness," he said. "At the center of all life, sleep plays an important role in determining key health outcomes. Sleep affects our wellbeing across the spectrum, from physical health to mental health. As such a large determinant of our quality of life, it is critical that people get the best quality sleep—and it’s surprising to find how rare this actually happens."

While wearables are not always 100% accurate, "they can be beneficial for analyzing your long-term sleep patterns over an extended period of time," Dr. Pietro Luca Ratti, a sleep expert for Australian company WhatASleep, said in an email interview. "Keeping track of your sleep patterns by memory is tough. The nights will begin to blend, and you will not get an accurate representation of the important things when it comes to sleep."

Ratti also suggests using a sleep journal to keep track of your sleep. "Whatever you use, it’s important to do it every night and do it over an extended period of time before making any decisions or having things analyzed," he said.

Better Tracking, Better Sleep

Cut down on screen time for better slumber, advised Dr. Chris Airey, the medical director of Optimale, in an email interview. 

"The less you have to think and the less you have to look at blue-light emitting screens, the better," he added. "If you have to fiddle with a sleep tracker on your phone, you could have trouble falling asleep due to blue light and even the stress of the new habit. Smartwatches are a great way to automatically track sleep, steps, and heart rate without needing to do much beyond initial setup."

The best way to track sleep at home is by using a smart mattress and a sleep tracking pod, sleep science coach Alex Savy said in an email interview. 

"Such an approach would result in full-body monitoring and a more extensive analysis of your sleep," he added. "I don’t believe a smartwatch can replace a sleep lab. The sensors that modern wearables use are quite advanced, but still can’t guarantee the same precision you might get at a sleep lab."

Everyone’s sleep seems to be getting worse during the pandemic. It might be worth turning to a smartwatch to figure out what’s going on. Just don’t expect your wearable to give you the most beneficial results.