These sensors on my nightstand, under my mattress and on my wrists automatically capture all sorts of information overnight. I’m swimming in a sea of data—time in bed, time asleep, time it took to fall asleep, number of disturbances, percentage in light and deep sleep, snoring instances, average heart rate, average breaths a minute. The goal of all this: fix my groggy mornings.
The pandemic has left me feeling perpetually in sleep debt and, apparently, I’m not alone. Can any of these smart bracelets, watches, pads or bedside smart displays help me wake up feeling more rested and refreshed?
Sleep tracking has long been offered on wearable devices such as Fitbit but, recently, more gadget makers are entering the bedroom. Last September, the Apple Watch got a sleep-tracking app with WatchOS 7. Google’s recently announced next-generation Nest Hub, which starts shipping Tuesday, has a radar sensor designed to measure nighttime movements and even breathing patterns.
The trackers are drawing attention to an often overlooked, yet vital aspect of our health, which sleep experts told me is a good thing. But the doctors and psychiatrists I spoke to also cast doubt on the devices’ ability to capture certain data, such as sleep stages, accurately, and said people can become easily overwhelmed by the data deluge—leading to more sleep-blocking stress.
Most sleep-tracking devices capture the basics: when you fall asleep, when you wake up and how much time between those events you spent snoozing. That sleep duration data is pretty comparable to research-grade devices, says Aric Prather, an associate professor of psychiatry at the University of California, San Francisco, who treats insomnia. Beyond that, every device has its own method and perspective on sleep tracking, including the five devices I tested.
The Apple Watch ($199 and up) takes a minimalist approach. The emphasis is on setting your time-asleep goal and sleep schedule, then holding you to it. The iPhone’s Health app, which displays average sleep over time, doesn’t provide analysis about the quality or length of your sleep. It will, however, nudge you when it’s time to wind down for bed.
Google’s Nest Hub ($100) is a smart display that can detect motion and breathing. There’s no camera—just an onboard radar sensor to capture your time asleep, restless periods, snoring disturbances and other data. The Nest Hub can track one person’s sleep, which means if you have a co-sleeper, they’ll need their own. And if it picks up snoring, it might not know that it’s your partner (as it is in my case), not you, who is doing it.
Withings Sleep Mat ($80) is an under-mattress pad that can sense tosses and turns, as well as breathing disturbances, such as snoring or prolonged pauses. It matches the sound of snoring with your respiratory patterns, so it can distinguish your snoring from your partner’s. Every morning, the Health Mate companion app assigns you a sleep score, based on how well it thinks you slept. You can also dive into other metrics, including how long you spent in deep and light sleep phases.
While all of Fitbit’s devices can track sleep, I tried the Sense smartwatch ($280). The app shows sleep-phase data and scores your sleep, like the Withings mat. A $10-a-month Premium subscription unlocks more detailed sleep score insights. For example, how your average nighttime heart rate factors into the grade.
Whoop ($18 a month and up) is a bracelet, included in the subscription price, with an optical heart-rate sensor and accelerometer. The app uses resting heart rate and heart-rate variability (the variation in time between heartbeats) captured during sleep to determine how hard you should train each day to prevent injury and illness.
There are numerous other trackers, including the NBA-endorsed Oura ring, which my fellow tech columnist Joanna tested for its ability to potentially predict Covid-19. But, frankly, there’s only enough data I could handle this week. Plus, there is such a thing as sleep-data overload.
The formal medical term is orthosomnia. “Basically, it’s insomnia from sleep-tracking devices,” said Dr. Prather.
Susheel Patil, a clinical doctor with the Johns Hopkins Pulmonary Sleep Medicine Program, had a patient with insomnia symptoms cure his sleeplessness by removing the Fitbit he was wearing every night. “It can be so much data, and we don’t know what to do with it. Unplugging can be more helpful,” Dr. Patil said.
Plus, seemingly “bad” results might not be meaningful. If your tracker says your sleep is fragmented, but you feel fine, it’s nothing to worry about, he added.
Another concern is the devices’ accuracy. “The gold standard is the polysomnogram with an EEG signature, and everything else is an estimate,” said Kelly Baron, director of the Behavioral Sleep Medicine Program at the University of Utah. An electroencephalogram (aka EEG) test, typically conducted in a lab, looks at electrical activity in your brain using nodes attached to your scalp.
I wanted to see how my data might compare with a polysomnogram test, so I sent Dr. Baron one night’s worth of my data captured by different devices. Looking at the sleep-phase data from Whoop and Fitbit, she said, “The staging data doesn’t look much like the stages we would see in a sleep study.” (The Apple Watch and Google’s Nest Hub don’t attempt to discern the different phases, and I hadn’t yet begun testing the Withings Mat, which does display sleep-cycle duration.) Dr. Baron pointed to the app’s record of a long period of REM—aka rapid eye movement—toward the end of sleep, and the small amount of time in deep sleep as unusual, even for a particularly terrible night of sleep.
Fitbit’s lead sleep scientist, Conor Heneghan, said its devices, which use heart rate to track sleep stages, adhere to clinical definitions of sleep as defined by the American Academy of Sleep Medicine, and were validated in labs against sleep studies. Still, he said, wearing a Fitbit “isn’t as good as going to a sleep lab, but it’s useful for tracking sleep in the real world, and tracking trends over time.” Dr. Heneghan added that wearing the wrist-based device too loose at night will decrease signal quality.
Whoop’s vice president of data science and research, Emily Capodilupo, said sleep-stage duration is presented to users who may be interested in the data, but it doesn’t factor into the calculation of the recovery score. She pointed to a peer-reviewed study, completed at the University of Arizona and funded by Whoop, that concluded Whoop’s sleep-staging analytics were comparable to results from a polysomnography test.
Of more indisputable value is trackers’ ability to spot signs of sleep apnea, “which is a huge drain on the medical system,” said Dr. Prather. Apnea affects a person’s ability to breathe during the night, and can lead to excessive daytime sleepiness and other serious health issues. Snoring and fragmented sleep are two symptoms that can show up in sleep-tracker data.
Both the Withings Mat and Google Nest Hub detect snoring and Fitbit’s CEO said that apnea detection is coming to his wearables. The Google Nest Hub revealed how much my husband’s snoring matched up with my restless periods. (I’ve worn ear plugs since.)
I found Whoop to be the most interesting, because the app isn’t just focused on sleep. It uses my last night’s sleep to make recommendations for the day ahead: whether I should go on a more strenuous bike ride or a leisurely walk through the park. But it’s overkill for people who aren’t interested in optimizing for athletic performance.
The biggest benefit of these trackers generally is that I’m now prioritizing my sleep, instead of merely thinking of it as the bookend to my day. And honestly, you don’t need trackers to do the same, and follow the two key tenets of the sleep experts I talked to:
Set consistent bed and wake times—even on the weekends.
Get seven to eight hours of sleep every night.
“Most clinicians, we’re a little bit guarded about the data,” said Dr. Patil. “But it at least gives people the opportunity to think about sleep.”
