Health on the wrist: wearables challenge medical devices, here are the limits

The watch that inflates on the wrist to measure blood pressure, the bracelet that reads it continuously, the ring that tracks sleep, stress. The earphones that become hearing aids. Within a few years, the market has pushed wearables to new frontiers of health. Functions and reliability are growing. But to what extent? The limitations compared to larger, more traditional medical instruments are undoubted, as confirmed by several studies published in PubMed in recent years, doctors and experts alike. It would be wrong, however, to snub this wave of innovation. Wearables are now a support that is really useful and even potentially life-saving in certain cases. For the prevention of heart problems for example.

The latest innovation concerns blood pressure measurement. The new Huawei Watch D2 smartwatch is capable of 24-hour ambulatory-type blood pressure monitoring. Unlike other similar products, it is not limited to optical sensors for measurement but has an inflatable micro-bracelet in the wristband.

A study published in 2025 compared the Watch D2 with a traditional system and found negligible differences in measurements. If we are only interested in measuring blood pressure on a continuous basis (for particular diseases), we can also consider wristbands that rely on optical readings (photoplethysmography). Among the best known is the Hilo and it is more convenient than a smartwatch for measuring blood pressure even while sleeping. The limitations of wristbands and smartwatches, however, are structural. Huawei itself explicitly states that the wrist must be within a defined circumference range. "You then have to hold your arm up with your wrist still at heart height. So it is more difficult to get correct measurements, compared to traditional sphygmomanometers,' explains Sergio Pillon, a cardiologist and pioneer of Italian digital healthcare. Measurement is even more degraded with optical reading wristbands.

Cardiac values were the first to be measured by wearable technology. The Apple Watch gives both notifications of irregular rhythms, based on optical sensors, and a one-track ecg app. The Apple Heart Study, involving more than 400,000 participants, showed in 2020 that about one third of users receiving an arrhythmia notification actually had documented atrial fibrillation. The limitation: a single ecg channel is very useful for intercepting certain arrhythmias, especially episodes of atrial fibrillation that would escape an ecg performed in an outpatient setting, but it cannot replace a clinical 12-lead trace nor an electrophysiological study. The quality of the signal then depends on contact, sweating, movement, and the user's dexterity.

It is therefore good to bear in mind that the device does not formulate a diagnosis, but signals the possibility of an arrhythmia and offers a means of recording a trace to show the doctor. The same approach can be found in other smartwatches equipped with a single-track ecg, such as Withings' hybrid models, which in Europe have obtained medical ce certification for detecting atrial fibrillation.