Researchers at ETH Zurich have built a handheld device that can tell whether your body is burning fat by measuring a substance called acetone in your exhaled breath. The device matches the accuracy of traditional lab tests for the same thing. It was developed under the supervision of Andreas Güntner and tested on 12 participants across different diet and exercise situations. The study was published in Device, a Cell Press journal, and ETH Zurich announced it on July 21, 2026. Engadget, ETH Zurich.

Here is the background in plain terms. When your body runs out of carbohydrates to burn for energy, it starts burning fat instead. This state is called ketosis. One byproduct of that process is acetone, which you breathe out. So measuring acetone in your breath gives you a window into whether your body is burning fat. Until now, confirming ketosis meant either a lab test or pricking your finger to draw blood. This device replaces all of that with a single portable gadget.

The main engineering challenge was making sure the breath sample stays clean. Earlier portable acetone detectors gave inaccurate readings because moisture and other particles in breath interfered with the sensor. The ETH Zurich team solved this by filtering out moisture and contaminants before the sample reaches the sensor. Cell Press / Device, Engadget.

A smartphone app walks the user through the breathing process. How hard you blow into the device and when the sample is collected are the two things most likely to throw off a reading. The app detects if you are blowing too hard or too softly and adjusts the timing to compensate. That back-and-forth between the app and the device is what sets it apart from a simple sensor that just takes a reading and nothing more. Engadget.

In the study, the device's acetone measurements closely matched lab results across all 12 participants, who were tested under various diet and exercise conditions. That match to lab-quality results is what separates this device from earlier consumer breath sensors, which were only roughly accurate at best.

The device is already on the market under the name Nutrion, sold by a company called Alivion. Engadget. New Scientist also reported on the study, with coverage dated August 25, 2026.

The broader context here is that we are seeing two trends converge: lab equipment shrinking down to handheld size, and health devices pairing with smartphone apps to give people real-time feedback on their own bodies. Over the past decade, continuous glucose monitors went from being clinical tools to something you can buy as a consumer. Acetone breath testing measures a related metabolic signal, and if it holds up in larger studies, it could follow a similar path.

It is worth flagging that 12 participants is a small group. Proving the device works in a controlled, small study is an important first step, but real-world differences in what people eat, how they breathe, and how their bodies metabolize food will test whether the filtering and app corrections still hold up at scale.

In this author's view, pairing a hardware sensor with software that actively manages the quality of each reading is the right design for this kind of device. It is the same approach that made continuous glucose monitors work well: the sensor alone is not enough without software correcting for how people actually use it. Whether Nutrion succeeds commercially depends on factors the study does not cover, but the engineering behind it is credible.