Will the Smart Ring detect an impending common cold? 🤒

Can an Oura Ring, Ultrahuman or Circular predict and warn of impending illness?

Will the Smart Ring detect an impending common cold? 🤒

Can an Oura Ring, Ultrahuman or Circular predict and warn of impending illness?

Some say yes. How is this possible?

And how did my test turn out?

That’s what this article is all about.

How can the disease be predicted?

Smart rings use sensors to measure a range of body metrics.

In particular, the following metrics are key to detecting (impending) disease:

  • 🌡️ Temperature
  • ❤️ RHR (resting heart rate at night)
  • 💗 HRV (Heart Rate Variability)

It may also be interesting to monitor respiratory rate, SpO2 and possibly derived sleep metrics such as disturbances etc.


I hardly ever get sick, thanks to my well-adjusted lifestyle. So I welcomed this virus, cold or whatever we want to call the common cold with open arms.

I wear an Oura ring as my primary ring. I also wore the Circular Slim and the Ultrahuman Air when I was tested for the virus.

1️⃣ Day one

The first day is absolutely crucial. It is the day when you feel more or less normal. Someone might have a hunch that something is wrong. I had one. I was a bit “heavy”, I wasn’t quite fresh.

And Oura confirmed my hunch (unfortunately or fortunately?) in Readiness, which she based mainly on a slightly elevated temperature. That is ➕0.6°C.

The other key metrics, RHR, HRV, are actually within the norm. For clarification, these are data from the night of “day one”.

For a long time, the Oura was primarily a night-time device, with daytime use as a pedometer or activity tracker. But that has changed recently. The Oura now tracks daytime stress very well and, fantastically, also calculates temperature in this metric. If it’s high, it displays it like this:

Oura’s daytime stress for the first day

I talk more about the stress functionality here:

Oura Ring Q4 2023 — Circles, stress, tags, experiments and more
The last time I exclusively covered the Oura Ring was in Spring 2023, when I mainly discussed the new Chronotype and…

What about the other rings that day?

Ultrahuman Air measured a smaller temperature deviation than Oura, only ➕0.17°C, so it pretends all is well. Circular Slim measured ➕0.57°C, which is almost exactly the same as Oura. However, it’s probably “low”. According to the information on the ‘temperature variation’ metric, it considers the +/- 0.8°C values to be something to pay more attention to.

2️⃣ Day two

On the second day, it was clear that I had a fever and was fighting something.

This was confirmed by the Oura ring and not only by the temperature (➕1.4°C), but also by ⬆️ RHR and ⬇️HRV:

Typical of the Oura ring, in similar situations it offers an activation called Rest Mode, which disables activity-related metrics so that you can focus primarily on rest.

A very similar finding was made for competitors, and I will recapitulate the Oura ring values for comparison:

  • Ultrahuman AIR: ➕1.42 °C, ⬆️ RHR = 58 bpm , but also ⬇️HRV = 45 ms*.
  • Circular Slim: ➕1.51 °C, ⬆️ RHR = 61 bpm , but also ⬇️HRV = 58 ms
  • Oura ring: ➕1.4 °C, ⬆️ RHR = 58 bpm , but also ⬇️HRV = 59 ms
    (*Ultrahuman calculates HRV differently than others)

3️⃣ Day three

On the third day the temperature peaked, which was measured quite reliably by all 3 rings.

  • Oura ring: ➕1.9 °C, ⬆️ RHR = 62 bpm , but also ⬇️HRV = 29 ms
  • Ultrahuman AIR: ➕1.86 °C, ⬆️ RHR = 58 bpm, but also ⬇️HRV = 28 ms*
  • Circular Slim: ➕1.50 °C, ⬆️ RHR = 62 bpm , but also ⬇️HRV = 37 ms

4️⃣ Day Four

The fourth day was marked by a decrease in the elevated temperature and a gradual return to values closer to baseline.

  • Oura ring: ➕0.8 °C, ⬆️ RHR = 51 bpm , but also ⬇️HRV = 55 ms
  • Ultrahuman AIR: ➕0.68 °C, ⬆️ RHR = 49 bpm, but also ⬇️HRV = 46 ms*
  • Circular Slim: ➕0.51 °C, ⬆️ RHR = 62 bpm , but also ⬇️HRV = 66 ms

5️⃣ Day five and six

The fifth day was similar to the first, my condition was not 100%, but I was fully functional, but I planned a very light activity — a walk.

On the sixth day, the situation was completely stable and the values were normal.

What can we conclude?

We could conclude that the smart rings measured very similar values, and at least the trend of temperature, night resting heart rate and HRV is the same. However, Oura predicted the illness a day in advance.

And that brings me to a point that has already been made on this channel. That is that a good piece of hardware, a pretty fancy smart ring, can be made by anyone today. It’s just that the software, the algorithms in the background, actually the weighting of the individual metrics for the final recommendation, Oura does that very well because of its years of lead and know-how. The other ring manufacturers are still catching up and will continue to do so for some time.

Here’s another quite interesting visualisation of the whole disease process in terms of temperature changes measured by the Oura ring. The numbers represent days.

I’m going to put it a little differently, and I’m going to allude in part to an argument like:

“I don’t need wearable electronics to tell me how I feel.”
Common ignoramus

Wearable electronics, smart rings, watches, etc. give you biofeedback, give you a different insight, a different perspective. Biofeedback doesn’t always match how you feel. Sure, it has its pitfalls, it can be a good servant and a bad master. It’s all about using and sometimes combining your feelings, your needs and this biofeedback.

In this article I have talked about illness. Again, some might argue, “I can tell when I’m sick and I’ll adjust my training program accordingly”.

However, I would like to emphasise the borderline moments of illness, i.e. the onset and the end of illness. Knowing that something is sneaking up on you, you can optimise a lot of things and help shorten the duration of the illness. On the other hand. For you, these last few days may mean that your body measurements are already normal and that you can return to your routine.

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