Wearable Biosensors Are Getting Serious: A Look at What Is Coming

The first time a consumer device detected a medical condition in the wild was 2018, when Apple released an ECG feature for the Apple Watch Series 4. Within months, the internet filled up with stories of people whose watches had detected atrial fibrillation, sometimes in people who had no prior symptoms at all. The FDA had cleared the feature. A wrist-worn device was now a cardiac screening tool.

What has happened in the years since has been quieter but arguably more significant.

The category of wearable biosensors has expanded considerably beyond step counting and heart rate. Continuous glucose monitors, which measure blood sugar through a small sensor inserted just beneath the skin, have become standard care for Type 1 diabetics and are increasingly being adopted by Type 2 patients. The Dexcom G7 and Abbott FreeStyle Libre 3 can connect to a smartphone and share data in real time with a physician, removing the need for constant finger pricks and enabling a kind of passive, continuous monitoring that was not possible a decade ago.

Blood pressure wearables have been harder to crack. The challenge is that accurate blood pressure measurement requires occlusion of blood flow, which a standard watch band cannot do. Samsung and Withings have released devices that use photoplethysmography to estimate blood pressure from wrist pulse waveforms, but accuracy varies significantly between users. The FDA has been cautious about clearing these devices for medical use, and most remain marketed as wellness tools rather than diagnostic ones.

The more interesting frontier is what researchers are trying to detect before symptoms appear. A team at Stanford published work in 2020 showing that data from consumer wearables could detect the onset of COVID-19 an average of two days before symptoms developed, simply by tracking heart rate variability and sleep patterns. Similar research has suggested that subtle changes in movement patterns, detectable by a standard accelerometer, may correlate with early Parkinson's disease.

The problem is not the sensing technology. It is the interpretation layer. A wearable device can generate enormous amounts of physiological data, but turning that data into accurate, actionable medical information is genuinely difficult. The human body is noisy. Heart rate variability changes with stress, caffeine, sleep quality, and dozens of other factors that have nothing to do with disease. Building algorithms that can distinguish signal from noise across a heterogeneous population is an unsolved problem.

There is also a question of equity. The devices most likely to detect conditions early are also the most expensive. And the populations most likely to benefit from early detection are often the least likely to own a smartwatch.

The trajectory of this field is genuinely exciting. What is coming in the next five years, continuous monitoring of hydration, respiratory rate, cortisol levels, and potentially even specific biomarkers through sweat analysis, will fundamentally change what it means to track your health passively, every single day.