Rings, bands and recovery
Do smart rings actually work?
Yes for sleep, on one brand, in one study. No for steps, where nobody has measured a ring at all. The honest answer is narrower than the marketing and better than the skepticism.
We earn a commission when you buy through our Amazon links, at no extra cost to you. It never decides a ranking — the rubric that does is published in full, so you can check us rather than take our word for it. How this works.
Top pick
Sleep staging you can actually citeOura Ring 4
The only consumer sleep device with a strong independent PSG result behind it — 76.3% four-stage agreement, and the best deep-sleep sensitivity of the three tested.
Price as of October 22, 2026. Prices move; Amazon's is the one that counts.
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The short answer
For sleep, yes - and the evidence is specific rather than general. In a 2024 inpatient polysomnography study the Oura Ring matched the sleep lab on seven of eight nightly summary measures and beat an Apple Watch on deep-sleep sensitivity, 79.5% against 50.5%. For step counting, exercise recording and anything explosive, a ring is the wrong device, and no study has measured a ring's step count at all.
Ranked
Quick picks
| # | Device | Best for | Evidence | Score | Price |
|---|---|---|---|---|---|
| 01 | Oura Ring 4 The only consumer sleep device with a strong independent PSG result behind it — 76.3% four-stage agreement, and the best deep-sleep sensitivity of the three tested. | Sleep staging you can actually cite | Peer-reviewed validation | 8.0/10 | $349.00Amazon |
| 02 |  RingConn Gen 3 A fortnight of stated battery with no fee of any kind — and not one published measurement of anything it reports. | Wearing it and forgetting about it | No validation study exists | 6.9/10 | $349.00Amazon |
| 03 |  Ultrahuman Ring PRO The longest stated battery and the most hardware of any ring here — from the only ring maker publishing measurement work, none of which was run on this ring. | Buyers who want the longest stated battery with no mandatory fee | No validation study exists | 6.8/10 | $479.00Amazon |
#ad· Live prices from the Amazon Product API, as of October 22, 2026. Where we have no verified live price we show none. Scores come from the published rubric at How we rank — the Evidence column shows what each ranking actually rests on, including where the answer is nothing.
The physics is genuinely on a ring's side
Every optical tracker does the same thing: shines light into tissue and infers pulse from what comes back. How well that works depends enormously on where you do it. A finger has more superficial arterial flow and less tendon, bone and movement artifact between the sensor and the blood than a wrist does.
The published record supports that reasoning rather than merely being consistent with it. A 2025 placement study of 28 participants wore identical sensors at wrist, forearm and upper arm against a chest strap and found the wrist the worst position by a wide margin - a bias near 33 bpm on the wrist-worn watch during explosive work, against under 0.1 bpm for a forearm sensor on a graded treadmill protocol. That study did not test a finger, so it is not direct evidence about rings. It is evidence that position matters a great deal, which is the premise.
The direct evidence is Robbins et al. (2024): 35 healthy adults, one night of inpatient polysomnography, wearing an Oura Ring Gen3, an Apple Watch Series 8 and a Fitbit Sense 2 at once. The ring posted 76.3% four-stage agreement (kappa 0.65) against the watch's 75.0%, and 79.5% deep-sleep sensitivity against 50.5%. It matched the lab on seven of eight nightly summary measures, missing only sleep latency by five minutes. The authors' own limits: one night, lab conditions, healthy adults without insomnia, and the comparison was made only during scheduled sleep.
A second paper backs the heart-rate side up. Dial et al. (2025) ran 536 nights across five devices against a Polar H10 ECG reference. The Oura Gen 4 returned 0.99 agreement and 5.96% error on nocturnal HRV, the best in the paper - ahead of a Whoop 4.0 at 0.94 and 8.17%, and well ahead of a Garmin at 0.87 and 10.52%, which the authors described as poor agreement.
What rings do not do, said plainly
Steps.No study has compared a ring's step count against a wrist device or a reference, and we say so on step accuracy by device. There is a structural reason to be skeptical beyond the missing study: a step is detected from acceleration, your hand swings differently from your hip, and a ring on a hand pushing a shopping trolley or holding a coffee is in a very different mechanical situation from a wrist. Pooled across 249 validation studies the 2024 umbrella review puts step count error from -9% to 12% for wearables generally - which is the metric the field is best at, and still a band wide enough to make between-device comparisons meaningless.
Exercise.A ring has no GPS, no screen and nothing to show you mid-session. It cannot pace an interval, record a route or hold a heart-rate band in front of you. If you lift, Oura's own guidance is to take the ring off - and a tracker you remove for training is not tracking your training. For explosive work, the placement study found every optical device tested fell below 0.50 concordance, and a ring is an optical device.
Anything medical.RingConn's own page states that its product is not a medical device, which is worth reading directly next to its apnea-pattern and vascular-health features. Treat every screening-flavored output from any ring as a prompt to see a clinician, not as a finding.
The subscription question, answered per brand
"Do smart rings need a subscription" is one of the most-asked questions about the category and the answer is genuinely different for each of these three.
Oura - yes, effectively. Oura publishes $5.99 a month or $69.99 a year with the first month free, and states that without it "your Oura Ring and Oura App will still function, but the insights, personal health data, and benefits you receive will be much more limited." Three years at the monthly rate, from the live price: $559.
RingConn - no, and nothing hidden behind a tier. RingConn states up to 14 days of battery plus a wireless charging case, 10 days of offline storage, a 2.3 mm profile at 2.5-3.5 g, and no fee of any kind. Three years is the sticker: $349. The honest counterweight is on the next line.
Ultrahuman - no mandatory fee, with an asterisk. Core tracking carries no subscription, but some app modules are billed monthly, from $2.90. The hardware is the most specified of the three: Ultrahuman states up to 15 days of battery (up to 45 with the charging case), 100 m water resistance and up to 250 days of on-device storage. Three years: $479.
The uncomfortable part: two of three have never been measured
Our ranking puts the Oura first and it is not close, for one reason: it is the only ring on this page with an independent result of any kind. No validation study exists that we could find for the RingConn Gen 3, or for the Gen 2 before it, or for the Ultrahuman Ring PRO.
Ultrahuman is the interesting case, and it deserves precision rather than dismissal. It is the only ring maker to have published measurement work at all: a 2026 preprint testing a VO2max estimate against cardiopulmonary exercise testing in 101 people, and a peer-reviewed 2026 analysis of 442 of its own users. Both were authored entirely by Ultrahuman employees, neither touches sleep staging - the metric buyers are actually paying for - and both tested the outgoing Ring AIR, whose PPG sensor Ultrahuman itself describes as redesigned for the PRO. So the research is real, worth reading, and does not transfer to the product on sale.
It is worth stating a limitation of our own rubric here rather than hiding it: our five-rung evidence hierarchy has no tier for "the manufacturer ran a real study with a real method". Ultrahuman lands at the floor alongside a company that has published nothing, and that is a weakness in the scale rather than a verdict on the ring. The three-way comparison is at Oura vs RingConn vs Ultrahuman.
So should you buy one?
Buy a ring if your question is about sleep and recovery, you want something you will genuinely wear every night, and you accept that one brand carries the evidence and the fee while the others carry neither. Buy a watch if you train with targets, need a screen, or want one device - the form-factor comparison with the numbers for both is at smart ring vs watch for sleep tracking.
And buy neither if what you actually want is a verified heart-rate number during exercise. No ring measures that well, because no optical sensor anywhere does. The ranked field is at best smart rings, and the wider sleep field - rings, watches and bedside devices together - is at most accurate sleep trackers.
In full
Every pick, and why
Oura Ring 4
The only consumer sleep device with a strong independent PSG result behind it — 76.3% four-stage agreement, and the best deep-sleep sensitivity of the three tested.
- Form
- Ring, worn on the index finger
- Sizing
- Size-specific — the ASIN is per size
- Subscription
- Membership required for full app features
What's good
- Robbins et al. (2024): highest four-stage agreement (76.3%, κ = 0.65) and best deep-sleep sensitivity (79.5%) of the three devices tested against polysomnography
- Matched PSG on seven of eight nightly summary measures, missing only sleep latency by five minutes
- A finger is a better optical site than a wrist for the same reason a forearm is
What isn't
- The membership is mandatory for the full app, so the sticker price is not the price — see our three-year arithmetic
- Rings are sized, so you need the sizing kit first and the ASIN varies by size
Skip this if
Skip this if you lift heavily. A rigid ring on a loaded barbell is uncomfortable at best, and Oura's own guidance is to take it off — a tracker you remove for training is not tracking your training.
What the evidence says
Peer-reviewed validationRobbins et al., Sensors 24(20):6532 (2024), n = 35, single-night inpatient polysomnography, testing the Oura Ring Gen3. Note the study tested Gen3, not the Ring 4. Note also that the manufacturer's press release rounded the four-stage figure to 79%; the paper says 76.3%. We use the paper.
Show how this 8.0 was calculated
| Factor | Weight | Score |
|---|---|---|
| EvidenceThe strongest peer-reviewed sleep result of any consumer device we found — with the honest caveats that it was one night, 35 people, and the previous generation. | 30% | 9.0 |
| HardwareFinger-mounted optical sensing, a better site than the wrist. | 20% | 8.5 |
| Metric coverageSleep, HRV, temperature and readiness; weak on exercise recording. | 20% | 8.0 |
| EnduranceMulti-day battery in normal use. | 15% | 8.0 |
| Cost per capabilityThe mandatory membership makes the true three-year cost materially higher than the sticker. | 15% | 5.5 |
Price as of October 22, 2026. Prices move; Amazon's is the one that counts.
#ad · we may earn a commission from this link to Oura Ring 4
RingConn Gen 3
A fortnight of stated battery with no fee of any kind — and not one published measurement of anything it reports.
- Form
- Ring, titanium and epoxy resin
- Size and weight
- 2.3 mm thick, 2.5-3.5 g, manufacturer-stated
- Battery
- Up to 14 days, manufacturer-stated, plus a wireless charging case
- Sizing
- Sizes 6-15 — the ASIN is per size
- Subscription
- None
- Extras
- Sleep apnea pattern insights, vascular health insights, 10 days offline storage
What's good
- Manufacturer-stated battery of up to 14 days, plus a charging case, with no fee attached to any of it
- No subscription and no paid app modules, so the sticker price is the whole three-year price
- Apnea pattern and vascular insights are included rather than sold separately
What isn't
- No independent validation of any kind that we could find — the same gap the Gen 2 has
- RingConn publishes no water-resistance rating and no sensor list we could read, so this site quotes neither
- RingConn's own page states the product is not a medical device, which is worth reading next to the apnea and vascular features
Skip this if
Skip this if you want a number somebody has checked. It is the cheapest ring to own over three years and the most comfortable to live with, and every figure it shows you is unaudited.
What the evidence says
No validation study existsNo independent validation study exists for this device that we could find, and none exists for the Gen 2 either. RingConn has not published a validation of its own. In a category whose headline output is a four-stage sleep graph you cannot check yourself, that absence is the most important thing about the product.
Show how this 6.9 was calculated
| Factor | Weight | Score |
|---|---|---|
| EvidenceNothing published by anyone, including RingConn itself. Same position as the Gen 2. | 30% | 2.5 |
| HardwareRingConn's current generation, per the manufacturer's own specification: 2.3 mm and 2.5-3.5 g in titanium and epoxy resin. | 20% | 8.0 |
| Metric coverageSleep, apnea patterns, vascular trends, cycle and activity, with no feature paywall anywhere. | 20% | 8.5 |
| EnduranceUp to 14 manufacturer-stated days plus a charging case, second only to the Ultrahuman Ring PRO's stated 15 among rings on this site. | 15% | 9.5 |
| Cost per capabilityNo subscription and no paid modules. Over three years that is the strongest cost position in the category. | 15% | 9.5 |
Price as of October 22, 2026. Prices move; Amazon's is the one that counts.
#ad · we may earn a commission from this link to RingConn Gen 3
Ultrahuman Ring PRO
The longest stated battery and the most hardware of any ring here — from the only ring maker publishing measurement work, none of which was run on this ring.
- Form
- Ring, unibody titanium with a PVD coating
- Size and weight
- 2.65 mm thick, 3.3-4.8 g by size, manufacturer-stated
- Battery
- Up to 15 days, up to 45 with its charging case, manufacturer-stated
- Water resistance
- 100 m / 328 ft, manufacturer-stated
- On-device storage
- Up to 250 days, manufacturer-stated
- Sizing
- Sizes 5-14 in four finishes — the ASIN is per size
- Subscription
- None required; some optional app modules are billed monthly
What's good
- Up to 15 manufacturer-stated days, and up to 45 with the charging case it ships with — the longest stated endurance of any ring on this site
- Up to 250 days of on-device storage against the four days of the ring it replaces, so time away from your phone costs you nothing
- A published 100 m water-resistance rating and a complete published specification table, which neither rival publishes in a form we could read
- Core tracking carries no mandatory fee, and Ultrahuman is the only one of these three makers to have published measurement work of any kind
What isn't
- Nothing has been published about this ring by anyone — Ultrahuman's two 2026 papers tested the outgoing Ring AIR, whose PPG sensor Ultrahuman says it redesigned for this one
- Nobody, including Ultrahuman, has published a sleep-staging validation of any of its rings — the metric most buyers are actually paying for
- At 2.65 mm and 3.3-4.8 g it is the thickest and heaviest ring here, where the AIR it replaces was the thinnest and lightest
- "No subscription" is still not quite the whole story: some app modules are billed monthly, from $2.90
Skip this if
Skip this if you are buying on the strength of Ultrahuman's research. The research is real and worth reading, but the company selling you the ring wrote all of it, it is about VO2max rather than sleep, and it was run on the ring this one replaces.
What the evidence says
No validation study existsNo validation study of the Ring PRO exists that we could find, by Ultrahuman or anyone else. Ultrahuman has published more about its rings than either rival's maker has about theirs — a 2026 medRxiv preprint testing a VO2max estimate against cardiopulmonary exercise testing in 101 people, and a peer-reviewed 2026 Frontiers in Digital Health analysis of 442 of its own users — but both were authored entirely by Ultrahuman Healthcare Pvt Ltd and both tested the Ring AIR. Ultrahuman's own PRO-versus-AIR table describes the PRO's heart-rate sensor as a redesigned PPG, which is precisely the thing a validation exists to test, so those papers do not transfer to this device.
Show how this 6.8 was calculated
| Factor | Weight | Score |
|---|---|---|
| EvidenceNothing published about this ring at all. Half a point above a maker that has published nothing whatsoever, because Ultrahuman's method on the previous ring is at least written down and readable — and well below the tier where somebody outside the company checked the hardware you would actually buy. | 30% | 3.0 |
| HardwareUnibody PVD-coated titanium with a stated 100 m rating, a dual-core processor with on-chip machine learning, a redesigned PPG plus temperature and a 6-axis IMU, BLE 5.3 and a ProRelease cut-away mechanism, per the manufacturer's specification — bought at the cost of being the bulkiest ring here. | 20% | 8.5 |
| Metric coverageSleep with stages, recovery, stress, movement and workouts, heart rate, HRV and temperature, with up to 250 days held on the ring — but several extras still sit behind paid modules. | 20% | 8.0 |
| EnduranceUp to 15 manufacturer-stated days, and up to 45 with the case it ships with. Ultrahuman states the figure varies by mode, roughly 12 days in Turbo and 15+ in Chill. | 15% | 9.5 |
| Cost per capabilityNo mandatory fee, so the three-year figure is close to the sticker — but the sticker is $479 against $349 for the RingConn, and some modules are billed monthly on top. | 15% | 8.0 |
Price as of October 22, 2026. Prices move; Amazon's is the one that counts.
#ad · we may earn a commission from this link to Ultrahuman Ring PRO
Four things to settle before you order a ring
- Get sized first. Rings are size-specific and the listing is per size. A ring that spins on the finger breaks optical contact, and a ring that is tight is a ring you take off.
- Decide about the fee before you buy, not after. One of these three charges a mandatory membership; the other two do not. Over three years that is the biggest single number in the decision.
- Check what you will do about lifting. If barbell work is a regular part of your week, a rigid ring is the wrong form factor and a screenless band is the right one.
- Know which outputs are unaudited. Sleep staging has one published result, on one brand. Steps, readiness, apnea patterns and vascular insights have none, on any brand.
Questions
Frequently asked
Do smart rings actually work for sleep tracking?
One does, demonstrably. In a 2024 inpatient polysomnography study the Oura Ring reached 76.3% four-stage agreement and 79.5% deep-sleep sensitivity, matching the lab on seven of eight nightly summary measures. No other ring on this page has been measured against a sleep lab by anyone.
Do smart rings track steps accurately?
Nobody knows - no study has compared a ring's step count against a reference or against a wrist device. Across wearables generally, step error runs from -9% to 12%, and that is the metric the field performs best at. Do not buy a ring for step counting.
Do smart rings need a subscription?
It depends on the brand. Oura publishes a mandatory membership at $5.99 a month or $69.99 a year and states the app is much more limited without it. RingConn charges nothing. Ultrahuman requires no fee for core tracking but bills some optional app modules monthly from $2.90.
Is a smart ring better than a watch?
For sleep and overnight heart rate, the finger is a better optical site than the wrist and the published results favor the ring. For training - live pace, zones, GPS, anything you need to see mid-session - a watch does things a ring cannot do at all.
Show your working
Sources
Every one of these was read in full before it was cited. Where we could not access a paper, we do not quote its numbers.
- [1]Peer-reviewed validation2024Robbins et al., “Accuracy of Three Commercial Wearable Devices for Sleep Tracking in Healthy Adults”, Sensors 24(20):6532
Brigham and Women’s Hospital. n = 35 healthy adults, single-night inpatient polysomnography, testing Oura Ring Gen3, Fitbit Sense 2 and Apple Watch Series 8. Authors’ stated limits: one night, lab conditions, healthy adults without insomnia, comparison only during scheduled sleep, and device failures on 6 Apple Watches and 2 Fitbits.
- [2]Peer-reviewed validation2025Dial, Hollander, Vatne, Emerson, Edwards & Hagen, “Validation of nocturnal resting heart rate and heart rate variability in consumer wearables”, Physiological Reports 13(16):e70527
DOI 10.14814/phy2.70527. n = 13 healthy adults (7 male, 6 female, 33.2 ± 8.6 years) across 536 nights, each wearing an Oura Gen 3, Oura Gen 4, Polar Grit X Pro, Garmin fēnix 6 and Whoop 4.0 simultaneously against a Polar H10 single-lead ECG reference sampled at 1000 Hz. Authors’ stated limits: healthy adults only, no atrial-fibrillation population, proprietary and periodically-updated algorithms, and unequal night counts per device. The Garmin was dropped from the resting-heart-rate comparison because the 30-minute window it uses is not timestamped.
- [3]Peer-reviewed validation2025“Impact of Anatomical Placement on the Accuracy of Wearable Heart Rate Monitors During Rest and Various Exercise Intensities”, Sensors (Basel)
n = 28 (14 male, 14 female). Polar H10 chest strap as the reference. Compared Polar Verity Sense (forearm), Garmin Forerunner 55 (wrist) and three simultaneous Whoop 4.0 units at wrist, forearm and upper arm, across rest, cycling warm-up, burpees and a modified Bruce treadmill protocol.
- [4]Peer-reviewed validation2024Doherty, Baldwin, Keogh, Caulfield & Argent, “Keeping Pace with Wearables: A Living Umbrella Review of Systematic Reviews Evaluating the Accuracy of Consumer Wearable Technologies in Health Measurement”, Sports Medicine
DOI 10.1007/s40279-024-02077-2. An umbrella review: 24 systematic reviews covering 249 unique primary validation studies and 430,465 participants (43% female), across 11 biometric outcomes, with roughly 34 of 310 identified consumer wearables ever validated. Reported accuracy by metric: heart rate approximately ±3% (mean bias −3.39 bpm); step count mean absolute percentage error from −9% to 12%; energy expenditure mean bias −3 kcal per minute with error ranging from −21.27% to 14.76%. Authors’ stated limits: a temporal lag between device release and published research, the intrinsic bias of a tertiary synthesis, and heterogeneity of protocols, devices, criterion measures and statistics severe enough that the authors did not pool a meta-analysis.
- [5]Manufacturer specification2026Oura — published membership pricing
Manufacturer-stated, read 2026-08-13: $5.99 USD/month or $69.99 USD/year before tax, with the first month free for new members. Oura states that without a membership “your Oura Ring and Oura App will still function, but the insights, personal health data, and benefits you receive will be much more limited.” Our three-year arithmetic uses the monthly rate — the less flattering of the two — and credits the free first month.
- [6]Manufacturer specification2026RingConn — Gen 3 published specifications
Manufacturer-stated, read 2026-09-06: from $349, sizes 6–15, titanium and epoxy resin, 2.3 mm thick at 2.5–3.5 g, battery “up to 14 days”, a universal wireless charging case, 10 days of offline data storage, vibration alerts, vascular health insights, sleep apnea pattern insights, and “No Subscription Required”. RingConn does not publish a water-resistance rating or a sensor list on that page in a form we could read, so neither appears anywhere on this site. The page also carries RingConn’s own disclaimer that the product “is not a medical device”.
- [7]Manufacturer specification2026Ultrahuman — Ring PRO buy page and published PRO-versus-AIR specification table
Manufacturer-stated, read 2026-09-06. Listed as a pre-order, “Shipping September 15th onwards”, with the Ring AIR still sold alongside it. Ultrahuman states up to 15 days of battery for the PRO (up to 45 with its case) against 4-6 days for the AIR, a dual-core processor with on-chip machine learning against single-core, up to 250 days of on-device storage against four, and a ProRelease emergency-removal mechanism the AIR does not have. We record it because buying the outgoing model in the week before a successor ships is a decision a reader should make deliberately. Re-read 2026-09-21: still listed as a pre-order, now "Shipping October 10th onwards" at $479, so the 15 September date slipped by more than three weeks; the Ring AIR is still sold alongside it. Re-read 2026-09-28, when the AIR had gone: this page and ultrahuman.com/ring/buy/us/ both configure a PRO only, at $479, still "Shipping October 10th onwards". Its published PRO-versus-AIR table is the source for every Ring PRO figure on this site — 2.65 mm thick (varies by size), 3.3–4.8 g, 100 m / 328 ft, sizes 5–14 in four finishes, up to 15 days of battery (roughly 12 in Turbo mode, 15+ in Chill) and up to 45 with the PRO Charging Case, a dual-core processor with on-chip machine learning, a redesigned PPG plus temperature and a 6-axis IMU, BLE 5.3, up to 250 days of on-ring storage, and ProRelease cut-away safety. Re-read 2026-10-19: the pre-order framing has gone — the buy page configures a PRO only, in four finishes and sizes 5–14, at $479, with no pre-order label and no shipping-date line anywhere on it; the only availability wording left is an FAQ entry saying “The ship-by date for your selection is shown on this page”. Ultrahuman does not state on the page when shipping actually began, so we do not either.
- [8]Manufacturer specification2026Ultrahuman — PowerPlugs add-on catalog and published prices
Manufacturer-stated, read 2026-09-06. This is why we do not call the Ring PRO flatly subscription-free: some app modules are billed monthly. Ultrahuman publishes Cardio Adaptability at $2.90/month, Cycle & Ovulation Pro at $3.99/month and Tesla Sync at $6.90/month, and states that “charges apply only to medical-grade experiences or partner-developed solutions”. Vitamin D, Smart Alarm, Caffeine Window, Social Jetlag, Screentime, Pregnancy Insights and the basic cycle module are listed as free, and core sleep, recovery and heart-rate tracking sits behind none of them. Re-read 2026-09-28 against the Ring PRO: all three monthly prices are unchanged.
- [9]Manufacturer claim only2026Dhawale et al., “Accuracy of a Smart-Ring VO2max Estimate and Five Published Prediction Equations Against Cardiopulmonary Exercise Testing”, medRxiv preprint
Posted 17 July 2026 and NOT peer reviewed — it is a preprint. All eight authors are employees of Ultrahuman Healthcare Pvt Ltd, the maker of the device tested, which is why it sits at the manufacturer tier here rather than beside the independent studies. What it did: 101 subjects measured against cardiopulmonary exercise testing (85 development, 16 held out), plus a population analysis of 181,133 deidentified ring users. With a self-reported fitness level supplied, the Ring AIR’s VO2max estimate agreed with CPET peak VO2 at a mean absolute error of 4.68 mL·kg⁻¹·min⁻¹ (95% CI 3.93–5.49), Pearson r = 0.79, Lin’s concordance 0.79 and a regression slope of 0.71. It measures VO2max. It does not test sleep staging. And it tested the Ring AIR: Ultrahuman replaced that ring with the Ring PRO in September 2026 and describes the PRO’s heart-rate sensor as a redesigned PPG, so this result does not carry over to the ring now on sale.
Read next
Related
- Best smart rings
The ranked field, with live prices and three-year costs.
- Smart ring vs watch for sleep tracking
The form-factor decision, with the published numbers for both.
- Oura vs RingConn vs Ultrahuman
The three rings on this page, head to head, including who wrote the research.
- Step accuracy by device
Why nobody can tell you how well a ring counts steps.