What data do smart rings collect, and where does it go?

What is physically in the ring

The hardware list is short, because there is not much room inside a 2 mm band.

• Photoplethysmography LEDs and a photodiode. Green light for pulse detection, infrared (and in some rings red) for blood oxygen estimation. The sensor measures how much light comes back as blood volume changes in the finger. Everything cardiac the ring reports starts here.
• An accelerometer. Movement, posture changes, step estimates, and - combined with the pulse signal - the raw material for sleep staging.
• A temperature sensor. Skin temperature at the finger, reported as a deviation from your own baseline rather than a clinical body temperature.
• A Bluetooth Low Energy radio. Ultrahuman lists BLE 5.3 for its ring; every ring here uses some version of it. This is the only way data leaves the device.

Some rings add extras - Circular advertises an ECG feature on its Ring 2 and NFC payments on its forthcoming Ring 3 - but the four above are the common core. There is no cuff, no electrode array and no glucose sensor in any consumer smart ring on sale, which is why the FDA has warned specifically against using smartwatches or smart rings to measure blood glucose.

What gets derived from those signals

Everything in the app that is not pulse, motion or temperature is calculated. Heart rate variability comes from the intervals between detected beats. Sleep stages come from a model combining pulse, HRV and movement - Altini and Kinnunen published the multi-sensor approach Oura uses. Blood oxygen comes from the ratio of red and infrared absorption. Readiness, recovery, stress and energy scores are brand-specific blends of all of the above against your own baseline.

That matters for privacy as much as for accuracy: the derived metrics are produced by the brand's software, often in its cloud, which is why the brand ends up holding a fuller picture of your health than the raw sensor data alone would suggest. We go through what each metric is worth on smart ring accuracy.

Where the data travels

The path is the same for every brand. Sensor readings are written to flash memory on the ring. When your phone is in range, the app pulls them over Bluetooth. The app sends them to the brand's servers, which run the analysis and send results back. What varies between brands is how much of that round trip is mandatory, where the servers are, and what the privacy policy permits afterwards.

The documents that answer those questions are the brands' own privacy policies - Oura's, RingConn's and Samsung's are all public and linked in our sources. We have not line-by-line audited each of them, and we say so rather than guessing: the clauses worth reading yourself, and what to look for in each, are set out on smart ring data privacy.

How long the ring holds data offline

This is the most under-documented number in the category, and it is the one that tells you how long you can leave your phone behind. Ultrahuman publishes the most generous figure: up to 250 days of on-ring storage for the Ring PRO, and up to a year of storage on the PRO Charger. Most other brands do not publish a figure at all, and in practice the answer for a typical ring is days rather than weeks before the oldest readings start being overwritten.

Either way, the ring shows you nothing while it holds the data - it has no screen. The full picture of what a ring can and cannot do without a phone nearby is on using a smart ring without a phone.

Accounts: what each brand requires

• Oura. An Oura account is required, and the membership is tied to the account rather than the ring. Without an active membership you see three daily scores - but Oura says you can still export all your data in CSV through the Membership Hub, and that cancelling does not delete anything unless you delete the account.
• Samsung Galaxy Ring. Samsung states that a Samsung account must be registered on your Samsung Galaxy smartphone to start using the ring. That is a harder requirement than any other ring here.
• RingConn. The RingConn app on iOS 17 or newer or Android 10 or newer, with no paid tier of any kind.
• Ultrahuman. No required subscription for data access; optional paid PowerPlugs add features.

What to look for if this matters

Four things separate a ring you can live with from one you will resent in a year.

1. Can you see your own raw data without paying? A paywall on derived scores is annoying; a paywall on the measurements is worse.
2. Is there an export? CSV export is the difference between borrowing your data and owning it.
3. What is the account requirement? A brand account plus a phone-brand account is two companies, not one.
4. Does the brand publish what it stores and for how long? Vagueness here is itself a data point.

The settings to check on day one

• Marketing and research consent. Usually set during onboarding, when you are not reading carefully. Go back and look.
• Health-platform sharing. Decide deliberately whether the ring writes into Apple Health or Google Health Connect. It is useful, and it is a second copy somewhere else - what Oura does and does not sync is on Oura HRV in Apple Health.
• Third-party integrations. Each one you enable is another company with a copy.
• Export, once. Do it in the first week so you know the route exists and what the file looks like.
• Account deletion path. Find it before you need it. Oura, for instance, puts delete-account-and-all-data in the Membership Hub alongside cancellation.

Mistakes people make

• Assuming the ring stores everything forever. It is a buffer, not an archive. The archive is in somebody's cloud.
• Confusing a derived score with a measurement. Readiness is arithmetic; pulse is a measurement.
• Believing a ring measures blood glucose or blood pressure directly. It does not - the FDA has warned about the glucose claim specifically, and we cover the blood pressure position on can a smart ring measure blood pressure.
• Never exporting. The day you want your history is the worst day to discover how to get it.