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.
There's this little light on the back of the device that shines into the blood vessels, and it uses the amount of light that is reflected back to estimate things like heart rate and heart rate variability, said Dr. Cathy Goldstein, a clinical professor of neurology at the University of Michigan who studies consumer sleep monitors.
Experts who study sleep trackers say that while there are some benefits to knowing this data, it can be presented in misleading ways, and they caution that sleep trackers aren't a cure for insomnia or other sleep disorders. Here's what to know about the trackers' capabilities and limitations.
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