Shawn McCall, 48, a personal trainer in Waterford, Michigan, started tracking his sleep almost six years ago. McCall said that his Oura Ring – a sleek titanium device that he wears on his ring finger – has revealed how the choices he makes during his waking hours affect his sleep at night.
“It serves as a constant reminder that if I do certain things, like have too much to drink or eat a large meal before bed, I know my heart rate is going to be higher that night and I’ll definitely have less deep sleep,” he said. “It helps keep me accountable.”
The popularity of consumer sleep-tracking technology has grown rapidly in recent years, and that growth is projected to continue. Led by wearable devices like the Oura, Fitbit and Apple Watch, the market also includes phone-based apps and “nearables”, which are placed on or beside a person’s bed.
Researchers have found that the latest sleep trackers are generally adept at detecting the basics: When a person is asleep or awake. However, Dr Goldstein said that trackers can be less accurate when collecting data from people with obesity or heart rhythm disorders such as atrial fibrillation, as well as from those who have darker skin tones, because skin pigment can interfere with the way light is reflected back to the device.
But even if the data collection is perfect, experts say that many of these technologies overreach when they attempt to translate findings into consumer-friendly takeaways.
“They’re presenting information with a granularity that they’re not yet capable of,” Dr Goldstein said.
For example, while many trackers offer data on a user’s sleep stages, such as REM sleep and deep sleep, these stages are defined by shifting patterns of brain activity – something most devices can’t directly measure.
“Inferring sleep and the sleep stages from peripheral phenomena like pulse rate or respiration has some inherent limitations, especially if the person is not healthy,” said Mathias Baumert, an associate professor of biomedical engineering at The University of Adelaide in Australia, who specialises in health technology.