What is the gold standard that wearables were compared against?
The study aimed to determine which wearables best track sleep stages: deep sleep, light sleep, REM sleep, and awake time. The researchers monitored 18 participants over five nights, each with different sleep conditions: normal sleep, restricted sleep, recovery sleep, and extended sleep. The participants wore multiple devices simultaneously, including popular brands like Apple Watch, Oura Ring, Whoop, Fitbit, and Garmin, as well as lesser-known options like the Circle Plus Ring and the Sleep 2 app (developed by the University of Salzburg).
To measure accuracy, researchers compared each device’s data to the gold standard in sleep science: polysomnography. This is a comprehensive test that records multiple physiological functions via a set of specialised sensors to measure brain activity, heart rate, breathing patterns, and eye movements while a patient sleeps.
Who are the overall winners?
The study identified three clear leaders. Their devices stood out for their high agreement with polysomnography, making them the best choices for most users.
Apple Watch excelled at detecting awake time and performed well for light and REM sleep, though it struggled with deep sleep accuracy.
Oura Ring was the most consistent across all sleep stages, particularly strong in tracking REM and light sleep.
Whoop (new algorithm) performed nearly as well as the Oura Ring, especially for REM and light sleep, but lagged in awake time detection.
The next two brands were middle of the road.
Fitbit (using its older algorithm) showed decent performance, particularly for REM sleep, but was not as accurate as the top three. The study noted that Fitbit’s newer algorithm, not tested here, may improve its standing.
Garmin was consistently mid-to-low tier, performing worse than the leaders but better than the lowest-ranked devices. It struggled most with REM sleep detection.
The Circle Plus Ring performed poorly across all metrics, making it the least reliable option in this study.
Nuances and surprises
Accuracy isn’t just about overall averages; it’s also about how well a device tracks changes in your sleep from night to night. The study found:
- Oura Ring and Whoop were best at detecting night-to-night variations in REM and light sleep.
- Apple Watch was the most accurate for awake time but less reliable for deep sleep.
- Fitbit and Garmin showed more variability, with Fitbit performing better for REM sleep and Garmin struggling with consistency.
No single device worked perfectly for everyone. For example:
- Some users found the Apple Watch highly accurate, while others ranked it lower.
- The Oura Ring had a similar split, with excellent results for some and average results for others.
- Whoop was the most consistent, rarely ranking as the worst but also not always the best.
- Garmin and Fitbit are not terrible, but they lag behind the top performers.
This variability means your personal experience with a device might differ from the average results.
Choosing the right device
There is a lot that goes into choosing your next wearable device, but if sleep tracking is among your top priorities, then this study can offer some guidance.
For overall accuracy: Oura Ring or Whoop (new algorithm) are your best bets.
For awake-time detection: Apple Watch is the clear winner.
For budget-friendly options: Wait for Fitbit’s new algorithm, early signs suggest it may close the gap with the leaders.
Avoid: The Circle Plus Ring based on this study’s findings.
Just note that this study, just like any other, has some limitations. For example, the study only had a small sample size of 18 people and did not include participants with severe sleep disorders.
