The most surprising thing to me about the Oura Ring 4, compared to its Gen3 predecessor, is how similar the two products are in terms of elemental usage perception. Granted, the precursor’s three internal finger-orientation bumps:

are now effectively gone:

and there are also multiple internal implementation differences between the two generations, some of which I’ll touch on in the paragraphs that follow. But they both use the same Android and iOS apps, generate the same data, and run for roughly the same ~1 week between charges.

One key qualifier on that last point: I bought them both used on eBay. The Ring 4, which claims 8 days of operating life when new, may have already accumulated more cycles from prior-owner usage than was the case with the Gen3 forebear, which touts 7 days’ operating life when new.

Smart ring “kissing cousins”

They look similar, too: the Gen3 in “Brushed Titanium” is the lower of the two rings on my left index finger in the following photos, with the Ring 4 in “Brushed Silver” above it:

And here’s the Ring 4 standalone, alongside my wedding band:

A smart ring enthusiast’s detailed analysis of the two product generations, complete with an abundance of comparative captured-data results, is below for those of you interested in more of an on-finger relative appraisal than I was able (and, admittedly, willing) to muster:

Sensing enhancements

Perhaps the biggest claimed innovation with the newer Ring 4 is Smart Sensing:

Smart Sensing is powered by an algorithm that works alongside the research-grade sensors within Oura Ring 4 to respond to each member’s unique finger physiology, including the structure and distinct features of your finger (i.e. skin tone, BMI, and age).

 The multiple sensors form an 18-path multi-wavelength photoplethysmography (PPG) subsystem, which adjusts dynamically to your lifestyle throughout the day and night.

As the functional representation in this conceptual video suggests:

there are two multi-LED clusters, each supporting three separate light wavelengths (red, green and infrared), with corresponding reception photodiodes in the rectangular structures to either side of each cluster (three structures total):

To complete the picture, here’s the inner top half of my Ring 4:

Six total LEDs, outputting to three total photodiodes, translates to 18 total possible light path options (which is presumably how Oura came up with the number I quoted earlier), with the optimal paths initially determined as part of the first-time ring setup:

and further fine-tuning is dynamically done while the ring is being worn, including compensating for non-optimum repositioning on the finger per the earlier-mentioned lack of distinct orientation bumps in this latest product generation.

What are the various-wavelength LEDs used for? Generally speaking, the infrared ones are capable of penetrating further into the finger tissue than are their visible-light counterparts, at some presumed tradeoff (accuracy, perhaps?). And specifically:

• Red and infrared LEDs measure blood oxygen levels (SpO2) while you sleep.
• Green and infrared LEDs track heart rate (HR) and heart rate variability (HRV) 24/7, as well as respiration rate during sleep.

All three LED types were also present with the Gen3 ring, albeit in a different multi-location configuration than the Ring 4 (albeit common to both the Heritage and Horizon Gen3 styles):

The labeling in the following Ring 4 “stock” image, by the way, isn’t locationally or otherwise accurate, as far as I can tell; the area labeled “accelerometer” is actually a multi-LED cluster, for example, and in contrast to the distinct “Red And Infrared…” and “Green And Infrared…” labels in the stock image, both of the clusters actually contain both green and red (plus infrared) LEDs:

Also embedded within the ring is a 3D accelerometer, which I’ve just learned, thanks to a Texas Instruments technical article I came across while researching this writeup, is useful not only for counting steps (along with, alas, keystrokes and other finger motions mimicking steps) but also “used in combination with the light signals as inputs into PPG algorithms.”

And there’s also a digital temperature sensor, although it doesn’t leverage direct skin contact for measurement purposes. Instead, it’s a negative temperature coefficient (NTC) thermistor whose (quoting from Wikipedia) “resistance decreases as temperature rises; usually because electrons are bumped up by thermal agitation from the valence band to the conduction band”.

Battery life optimizations

As noted in the public summary of a recent Ring 4 teardown by TechInsights, the newer smart ring has a higher capacity battery (26 mAh) than its Gen3 predecessor, which is likely a key factor in its day-longer specified operation between recharges. Additionally, the Ring 4’s Smart Sensing algorithms further optimize battery life as follows:

In order to optimize signal quality and power efficiency, Oura Ring 4 selects the optimal LED for each situation, instead of burning several LEDs simultaneously.

and

Smart Sensing also helps maximize the battery life of Oura Ring 4 by dynamically adjusting the brightness of the LEDs, using the dimmest possible setting to achieve the desired signal quality. This allows the battery life of Oura Ring 4 to extend up to eight days.

Here, for example, is a dim-light photo of both green LEDs in action, one in each cluster:

Generally speaking, the LEDs are active only briefly (when they’re illuminated at all, that is) and I haven’t yet succeeded in grabbing my smartphone and activating its camera in time to capture photos of any of the other combinations I’ve observed and note below. They include:

• Single green LED (either cluster)
• Concurrent single green and single red LEDs (one from each cluster), and
• Both single (either cluster) and dual concurrent (both clusters) red LED(s)

I’ve also witnessed transitions from bright to dim output illumination, prior to turnoff, for both one and two concurrent green LEDs, but not (yet, at least) for either one or both red LED(s). And perhaps obviously, the narrow-spectrum eyes-and-brain visual sensing and processing subsystem in my noggin isn’t capable of discerning infrared (or even near-IR) emissions, so…

Third-party functional insights

Operating life between integrated battery recharges, which I’ve already covered, is key to wearer satisfaction with the product, of course, as is recharge speed to “full” for the next multi-day (hopefully) wearing period.

But for long-term satisfaction, a sufficiently high number of supported recharge cycles prior to effective battery expiration (and subsequent landfill donation) is also necessary. To wit, I’ll close with some interesting (at least to me) information that I indirectly (and surprisingly, happily) stumbled across.

First off, here’s what the Ring 4 looks like in the process of charging on its inductive dock:

In last month’s Oura Gen3 write-up, I shared a photo of the portable charging case (including an integrated battery) that I’d acquired from Doohoeek via Amazon, with the dock mounted inside. Behind it was the Doohoeek charging case for the Oura Ring 4. They look the same, don’t they?

That’s because, it turns out, they are the same, at least from a hardware standpoint. Requoting what I first mentioned last month, the “development story (which I got straight from the manufacturer) was not only fascinating in its own right but also gave me insider insight into how Oura has evolved its smart ring charging scheme for the smart ring over time. More about that soon, likely next month.

Here’s the Ring 4 and dock inside the second-generation Doohoeek case (which, by the way, is also backwards-compatible with the Gen3 ring and dock):

And as promised, here’s the full back-and-forth between myself (in bold) and the manufacturer (in italics) over Amazon’s messaging system:

As I believe you already realize, while Doohoeek’s first-generation battery case that I’d bought from you through Amazon works fine with the Oura Gen3, it doesn’t (any longer, at least) work with the Ring 4. For that, one of Doohoeek’s second-generation battery cases is necessary. Can you comment on what the incompatibility was that precluded ongoing reliable operation of the original battery case with the Ring 4 charging dock (although it still works fine for the Gen3)? A USB-PD handshaking issue between your battery and the charging dock? Or was it something specific to the ring itself?

Hi Brian,

thank you for your question! Here’s a brief technical explanation of the Ring 4 compatibility issue with our original charging case:

Our first-gen charging case used a smart current-detection algorithm to determine charging status. Under normal conditions, when the ring reached full charge, the current would drop and remain consistently low—triggering our case to stop charging. This worked flawlessly with Oura Gen3 and initially with the Ring 4.

However, after a recent Oura firmware update, the Ring 4 began exhibiting unstable current draw patterns during charging—specifically, prolonged periods of low current followed by unexpected current spikes, even when the ring was not fully charged. This behavior caused our case to misinterpret the ring as “fully charged” and prematurely terminate charging.

To resolve this, we redesigned our charging logic in the updated version to implement a more robust timing-based backup protocol.

We appreciate your interest and hope this clarifies the engineering challenge we addressed!

Best,

Doohoeek Support Team

This is perfect! It was obvious to me that whatever it was, it was something that a firmware update couldn’t resolve, and I’d wondered if ring-generated current draw variances were to blame. I suspect the Ring 4 is doing this to maximize battery life over extended charge cycle counts. Thanks again!

p.s…I also wonder why you didn’t change the product naming, box labeling, etc. so potential buyers could have reassurance as to which version they’d be getting?

Hi Brian,

Thank you for your insightful feedback — you’ve clearly thought deeply about how these systems interact, and we really appreciate that.

Yes, the current behavior on the Ring 4 appears optimized for long-term battery longevity Read Original