Fitbit recently announced plans to build sleep apnea diagnostics into its wrist-worn activity tracking devices, stating that it expects do so within a year. If successful, Fitbit may be able to address a market that is expected to have $6.7 billion in revenue by 2021.

Sleep apnea is characterized by pauses in breathing and shallow breath and comes with an increased risk of heart failure, obesity, and strokes. While it affects about 18 million American adults today, one of the biggest concerns is that many affected people do not realize they are affected. Traditionally, sleep apnea diagnosis involved capturing electroencephalograms (EEG) using electrodes that track brain electrical activity. Such EEGs generally require cumbersome overnight visits to a sleep lab. Alternatively, although potentially not as definitive as EEGs, non-EEG based methods that combine cardiac, respiratory, and movement data may be used. However, alternative methods have not achieved broad use by the consuming public. According to its announcement, Fitbit aims to fill that gap in the market.

The fashion appeal of activity trackers and ease of use (i.e., simply wearing it) have fostered widespread adoption of activity tracking devices. Also, these devices have increased their functionalities over the years from merely counting steps to reporting heart rates and calories burnt, among others. It’s likely that these devices are here to stay and will get “smarter” and more capable. It may seem strange that “activity” trackers are seeking to carefully monitor inactivity, but they may prove up to the task — in fact, there is some evidence suggesting that the devices are better at measuring rest than activity.

In March, 2017, Fitbit released Sleep Stages, a feature that tracks whether the wearer is in a light, deep, or REM sleep. By combining heart rate analysis with more traditional movement tracking, a study found that it could determine sleep stages with a reasonable degree of accuracy. Fitbit has logged over 4 billion nights of sleep data, a data pool of over 23 million hours, from its users since 2010. However, reliable detection of sleep apnea may require a more advanced analysis than reliably categorizing sleep stages.

CNBC reports that Dr. Conor Heneghan, author of the study and Fitbit’s lead sleep research scientist, is researching additional data sources that Fitbit’s trackers may be able to exploit as potential indicators of sleep apnea. He explains:

We’re leveraging the fact that Fitbit has experience in optical electronics, and making them small and power efficient.

Fitbit’s activity/inactivity trackers will not cure or treat sleep apnea. Rather, CNBC reports that Fitbit seeks to provide reliable sleep apnea detection. Even if its forthcoming technically is sound, challenges may wait for Fitbit. The report notes that Fitbit isn’t yet certain how much it will need to work with the FDA and regulators in other countries. The device will most likely nudge a user to see a doctor rather than making a diagnosis. And, Roy Raymann, vice president of sleep science at SleepScore Labs, and the former sleep expert on Apple’s health team, opined that:

Doctors are often ultraconservative, so it remains to be seen whether they’ll accept data from a consumer wearable.