Heat Flux Wearables: The Missing Signal in Metabolic Health
Learn how Vire Clip uses heat flux and 24/7 body temperature tracking to explore metabolism, hormonal timing, energy expenditure and menopausal hot flashes.
- Written byGabriel Kolanen
- ExpertAntti Immonen
- Published
- Updated
- Reading time
- 6 min
Your body is producing and losing heat every second of your life. It is one of the most information rich things about you, and consumer health technology has very largely ignored it.
The first generation of wearables taught us to count steps, stage sleep, read a pulse, estimate blood oxygen and take a skin temperature. All useful. All measured from the wrist or the finger, and all built on two sensing ideas: optical heart rate and motion.
Heat was left out, which is strange, because heat is where the metabolism actually shows itself. Every process that keeps you alive produces it, and all of it eventually leaves.
A physiological brick wall
Around 2019, Antti Immonen and his team built a MEMS heat flux sensor, a micro-electro-mechanical device designed to read the precise amount of heat leaving the skin. Then they tried to put it on a watch and a ring, and ran into the body itself.
Hands and wrists are the body's radiators. They are also the most exposed part of you, waving through cold air, resting on a warm desk, in and out of pockets. Immonen describes the result as constant potential disturbing signals, chief among them environmental dependency.
Put plainly: a good deal of the time, a wrist sensor is telling you about the room rather than about you.
Turn your phone sideways to compare the two.
The same physiology, two places to read it from. The signal at the waist is not merely cleaner. It is continuous, which is what makes a rhythm legible at all.
So the team moved the sensor to the waist. Not because the waist is fashionable, but because it is central, close to the core, and stays covered. A device that stays covered stays on, and a device that stays on produces an unbroken line.
What heat flux actually is
Heat flux is the flow of thermal energy out of the body and into the world around it. It is not the same as temperature. Temperature tells you the level; flux tells you the rate at which heat is leaving.
This matters because of an awkward fact about exercise. When you work hard, most of the energy you burn does not become movement.
Turn your phone sideways for the full bar.
Proportions are indicative and vary with effort, fitness and conditions. The point is the ratio, not the decimal place.
In a laboratory, measuring that heat as it dissipates is how metabolism is assessed properly, inside a sealed calorimetric chamber. What the waist offers is not a chamber. It is a set of measurement points on the skin where that flow can be read continuously, while you get on with your day.
Those measurement points, in one picture. Heat leaving the skin, the moisture it carries with it, and the temperature on either side of that flow, all read from the same place and all read continuously.
Temperature has a shape, and the shape has a schedule
Your body runs on rhythms that took a very long time to evolve and which do not care much about your calendar. Cortisol climbs before you wake. Melatonin arrives in the evening. Temperature does not measure either of those, but it moves on the same clock, so its shape tells you when your own day is actually turning.
He describes continuous temperature as the most comprehensive non-hormonal proxy to those signals. Non-hormonal is the important half of that phrase. Nothing here is a hormone measurement. It is a curve whose turning points tend to line up with them.
Turn your phone sideways for the whole day.
An illustrative day, not exported data. The value is in where the turns fall, because those are the moments your own schedule can be built around.
Each of us has a slightly different version of this, and the same person has more than one. The shape of a night shifts with where you are in a longer rhythm as well as a daily one.
Average nightly temperature from Vire Clip wearers, follicular against luteal, with the spread around each. The same descent, the same climb, sitting at a different level. Group averages rather than any one person's record.
Knowing the tempo of yours is what lets you put the demanding things where your body is already climbing, and the quiet things where it is already coming down. Working with the rhythm rather than against it.
Widening the base
For more than a decade, wearables have rested on two measurements: light through the skin for pulse, and accelerometers for motion. Everything those devices tell you is built on that pair, which is also why so many of them tell you such similar things.
Our argument is that the next step is not a better algorithm on the same two signals. It is more signals.
Turn your phone sideways for both rows.
Not a better version of the same wearable. A wider base to build on.
Thermoregulation is one of the least continuously measured processes in the body, and that gap is the interesting part. It is also where the research goes next, including how thermoregulation changes across midlife, an area with far less continuous data behind it than it deserves.
That is a statement about what has not been measured, not a claim about what we can tell you. We are at the beginning of it, and we would rather say so.
A long craftsmanship project
Turning raw heat flux into something that changes what you do on a Tuesday is, in Immonen's words, a long craftsmanship project. The sensing is the part we have spent a decade on. Making the output worth opening is the work in front of us, and the people testing the Clip have been extremely clear that this is where the effort belongs.
The Vire Clip launches in November 2026. What it offers is not a new score. It is a signal your body has been broadcasting your whole life, that nobody has been close enough, or covered enough, to read all the way through.
Expert: Antti Immonen. Writer: Gabriel Kolanen. Published June 2026, revised September 2026.
The Vire Clip is a consumer wellness product. It is not a medical device, and it is not designed or intended to be used for fertility or conception analysis, or for the diagnosis, prevention, monitoring, treatment or alleviation of any disease or condition. Figures in this article are illustrative of the physiology described rather than exports of any individual's data.
