At TechRadar, I often find myself pitting wearables against each other. Next week, you’ll be able to read what happened when I took the Coros Vertix 2S, Garmin Fenix 8 and Oura Ring Gen 4 out on a 5k run at the same time. I performed a similar test when pitting the best smartwatches against Strava while running the 2024 London Marathon.
One aspect of health tracking I haven’t group-tested is sleep tracking. Fortunately, researchers from Harvard Medical School and Brigham and Women’s Hospital, Boston, have done the legwork for me by testing the Oura Ring Generation 3 against an Apple Watch Series 8 and Fitbit Sense 2, to see which one is the most accurate. To set a benchmark, the three devices were also tested against a gold-standard, medical-grade polysomnograph (a tool used to diagnose and measure sleep disorders).
Studying 35 participants, the results showed that all devices accurately detected sleeping and wakeful states. However, the Oura Ring was best at discriminating between sleep stages, matching the polysomnograph with about 80% accuracy.
Published in the journal Sensors, the researchers wrote: “The Oura ring was not different from PSG [the polysomnograph] in terms of wake, light sleep, deep sleep, or REM sleep estimation.
“The Fitbit overestimated light (18 min; p < 0.001) sleep and underestimated deep (15 min; p < 0.001) sleep. The Apple underestimated the duration of wake (7 min; p < 0.01) and deep (43 min; p < 0.001) sleep and overestimated light (45 min; p < 0.001) sleep.
“In adults with healthy sleep, all the devices were similar to PSG in the estimation of sleep duration, with the devices also showing moderate to substantial agreement with PSG-derived sleep stages.”
While all three devices were accurate when it came to tracking wakefulness and sleep, the Apple Watch was the least accurate at measuring sleep stages overall. It’s worth noting that this test was conducted before the release of the Vitals app on watchOS 11, which has changed the way Apple tracks sleep using an Apple Watch. The Fitbit Sense 2, on the other hand, hasn’t changed the way it tracks sleep, so we can expect this to still be accurate, as far as it goes.
It’s worth noting that with only 35 participants tested the results might not be statistically significant, but the study is a good indication of what smart rings can do. The Oura Ring was the only device that stuck to the PSG’s readings throughout different sleep stages, while the watches either over or underestimated.
This could be due to the ring’s positioning on the hand, rather than on the wrist. In my briefing with Jason Russell, VP of Consumer Software Product at Ōura, it was mentioned that the ring’s placement on the finger was beneficial as the LED has a smaller distance to reach while measuring the blood flow than if the sensor was trying to get through your wrist, ensuring a more accurate measurement overall. The new Oura Ring 4 also mitigates this by offering more “pathways” for the sensors’ lights to follow.
If this is the case, then all of the best smart rings, such as the Samsung Galaxy Ring, could be considered more accurate than smartwatches for heart rate measurement and sleep tracking. Samsung even reports increased accuracy when the Samsung Galaxy Watch 7 and Ring are used together. There’s also the aspect of being slightly more unplugged: wearing a smart ring instead of a smartwatch means there’s one less screen in your life, and they tend to last longer than many smartwatches: the Apple Watch Series 10 caps out at 18 hours, while the Oura Ring trucks along for around seven days.
I don’t think smartwatches are going to be entirely replaced just yet, though. Screens allow for a level of granularity and interaction that are just too useful for many people. This is especially important in the case of workouts: I use the screen on my best running watches to follow a preset route during runs and check my heart rate/pace at regular intervals. Just because a smart ring is slightly more accurate from a metrics perspective doesn’t mean it’s inherently more useful, and I could always pair my watch with one of the best heart rate monitors.
Nonetheless, a clinical study pitting the Oura Ring against not just other wearable devices, but a medical-grade PSG, means you can put your trust in its night-time metrics. It’s certainly a relief to Oura users: after all, those rings aren’t cheap and you want to know your expensive initial purchase (and ongoing subscription) is worth it.
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