O2Ring vs O2Ring S: What Actually Changed

If you already own a Wellue O2Ring, or you are about to buy one and have noticed there are now two of them, the question is simple: is the O2Ring S actually different, or is it the same ring with a new letter on the box? The honest answer is that it is a real upgrade, but a narrow one — three concrete changes, none of which touch the thing most people assume changed. Here is what is different, taken from the two devices' published specification sheets, and what it means on an actual night's sleep.

The short answer

The O2Ring S records four times more often, lasts about half again as long on a charge, and charges over USB-C. The ring itself is the same size and weight, worn the same way, with the same vibration alerts. If your current O2Ring works for you, the S is a refinement rather than a reason to replace it — the upgrade matters most if your nights run long, or if you care about catching very short oxygen dips.

O2Ring vs O2Ring S: the specs side by side

What the 1-second interval actually buys you

This is the change worth caring about. The original O2Ring writes a reading every four seconds; the S writes one every second. Oxygen desaturations during disturbed sleep can be brief — a dip that lasts ten or fifteen seconds is only three or four data points at the old interval, and a shorter one can be smeared into the readings on either side of it. At one-second resolution the same dip is drawn with fifteen points, so its true depth and shape survive into the report you look at the next morning.

In practice that means the S is less likely to under-represent how far a drop actually went. It does not find events that did not happen, and it will not turn a consumer wellness ring into a diagnostic tool — but if you are tracking overnight dips over time, or gathering data to show a clinician, a finer trace is genuinely more useful. For what those dips mean in the first place, see why SpO₂ drops during sleep.

Battery: 16 hours to 24

The published figure goes from 12–16 hours of typical use to up to 24. For a single eight-hour night neither is a constraint — both cover it comfortably. The difference shows up if you wear the ring during the day as well as at night, or if you would rather charge every third night than every second one. It is a convenience gain, not a capability gain.

USB-C

Small, but the kind of small that matters at 11pm. The original uses micro-USB; the S uses USB-C, which for most people now means the same cable as their phone or laptop. One fewer legacy cable to keep in the bedside drawer.

What did not change

The S is the same 15 g, the same 38 × 30 × 38 mm, worn on a finger or thumb the same way. It records the same things — oxygen level, pulse rate and motion — and it still buzzes on your finger when a reading crosses a threshold you set, which remains the O2Ring family's best feature for the person actually wearing it. Wellue describes the S as having improved signal filtering and more stable readings; that is a manufacturer claim rather than an independently verified result, so treat it as a reasonable expectation, not a measured guarantee.

The compatibility catch nobody mentions

Here is the part that does not appear on any spec sheet, and it is the one that generates the most confusion. The O2Ring S does not just have new internals — it speaks a different Bluetooth protocol than the original O2Ring. We know this because we had to implement it: adding O2Ring S support to OxyRemote meant writing a completely separate handler rather than reusing the existing O2Ring one.

Two practical consequences follow. First, an app that supports the original O2Ring does not automatically support the S — support has to be added deliberately, so a ring that pairs fine with one app may be invisible to another. Second, the S is genuinely harder for apps to discover: it advertises itself over Bluetooth without the service identifiers most apps scan for, and different production runs of the hardware advertise under different names. If your S shows up in the manufacturer's app but not somewhere else, that is usually the reason — not a fault in the ring.

So which should you buy?

• Already own an O2Ring and happy with it — keep it. Four-second data is perfectly serviceable for spotting overnight patterns, and nothing about the original stopped working.
• Buying your first ring — get the S if the price gap is modest. Finer data and a modern cable are worth having from the start.
• Wearing it during the day as well as overnight — the S, for the battery.
• Tracking dips carefully over time, or collecting data to show a clinician — the S, for the one-second trace.
• On a tight budget — the original O2Ring remains a genuinely good overnight monitor, and a discounted one is not a bad buy.

If you are still choosing across the wider Wellue and Viatom family rather than between these two, our O2Ring vs SleepU vs Checkme O2 Max comparison covers the other form factors, and the Checkme O2 Max review goes deeper on the wrist-worn option.

Both are still record-then-review devices

One thing the S does not change: like the original, it is built around recording the night and reviewing it in the morning. The data lives on the ring, syncs to the paired phone nearby, and gets read the next day. That is exactly right if you are monitoring yourself. It is the wrong shape if you are watching someone else — a parent in another house, a partner in another room — because by the time you see a low reading, the night is over. An app layer like OxyRemote reads either ring over Bluetooth and streams the numbers live to other people's phones, with a push alert the moment a reading crosses your threshold. The background on that setup is in viewing O2Ring data remotely, and the app comparison is in the best app for a Wellue O2Ring.

The bottom line

The O2Ring S is a genuine but narrow upgrade: one-second recording instead of four, up to 24 hours instead of 12–16, and USB-C instead of micro-USB, in the same ring on the same finger. The one-second interval is the reason to want it. The protocol change is the reason to check app support before you assume your existing setup will just pick it up. And neither ring, on its own, shows anyone but the wearer what is happening while it happens.