Less than half of Americans meet the recommended sleep goal of seven or more snoozing hours. Not good—sleep deprivation is associated with decreased alertness, cognitive impairment, stress, maintenance of body fat, and a litany of more severe health problems.
To capitalize on America's desire for more shut-eye, many health trackers have added automatic sleep monitoring to help users gauge length and quality. But various reports show that sleep trackers and apps can be wildly inaccurate—off by an hour or more.
To put these devices to the test, I compared the most popular consumer sleep tracking gadgets to the gold standard in laboratory sleep equipment, a polysomnograph (PSG).
Unlike wrist, waist, and phone apps that estimate sleep from movement, a PSG uses sensors to measure every known aspect of sleep: skull electrodes measure brain waves, eye patches track rapid eye movement, fingertip sensors measure blood oxygen, and limb sensors measure sleep paralysis. It took over an hour to hook myself up to the laboratory-grade equipment, which made me look like I’d just auditioned to be the stunt double in a Wolverine flashback scene.
Below are graphs with the most important results. It turned out that for me, most sleep trackers were fairly accurate for both total sleep and the stages of sleep.
Here's a key to understand the graph of accuracy:
● Lab: The polysomnograph, the benchmark for the other three.
● The Basis: Represents a wrist device with a resting heart rate monitor. It is the only popular consumer technology to measure both REM (which restores the mind) and deep sleep (which restores the body).
● The Jawbone Up: My all-purpose representative for the list of wrist-based movement trackers. The Fitbit, Nike Fuelband, and Misfit Shine are its closest competitors.
● The Sleeprate: A new heart rate chest strap device that purports to be the cutting edge of consumer sleep devices. The Sleeprate scientists are the ones who hooked me up to the PSG. (Note: They did not have access to my sleep rate data until after they showed me the data from the PSG.)
For the most common measures—sleep stages, quality, and total time—most of the devices were fairly accurate. The Basis was most inaccurate on time (by 23 minutes) largely because it didn't properly assess when I was asleep and when I was lying awake in bed. The Sleeprate was identical to the lab measure.
In terms of sleep stages, all the devices were close, with the Sleeprate being the most off (5 percent) because it had stricter standards for what counts as REM. Indeed, both the Basis and the Sleeprate were off by 5 percent in the measure of REM alone; but because the Basis also undershot the measure of deep sleep, it ended up being more accurate in combined sleep measures.
My scores for light, deep, and REM sleep were well within normal, but I still felt sleepy in the morning. I wanted to find out what else was screwing with my sleep at night. Only the Sleeprate accurately detected my sleeping problems. It turned out that I had dozens of sleep interruptions during the night, which likely caused me to feel sleepy in the morning. Neither the Basis nor the Up detected interruptions.
A closer reading of the Sleeprate dashboard found that both it and the PSG detected an elevated heart rate. (In other words, I was stressed out during the day and it was screwing up my sleep at night.)
So, what device is right for you? It depends on your particular problem, and a bit of self-hacking is necessary to figure out the issue. The first step is diagnosis. If duration of sleep is your problem, then a simple actigraph measure, like a smartphone sleep tracker, may work. If it’s a greater problem than just duration, I’d recommend trying the Basis watch for monitoring REM and deep sleep.
For me, it took the Sleeprate to show that daytime stress was the likely culprit of morning drowsiness. Daytime stress was hard to isolate, but I happened to attend Camp Grounded, a digital detox camp, last weekend, free of all electronics. To my surprise, I woke up feeling great.
Of course, I'm not going to wear a chest strap to bed every night, so I'll keep using a sleep tracker until I can figure out how to eliminate stress during the day.
Maybe then I’ll finally get some good shut-eye.