11/5/25

I/O Magazine

Smartwatches and fitness trackers are becoming useful clinical health tools, and privacy considerations are key

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Privacy in the Age of the Smartwatch

Heart rate. Blood pressure. Sleep measurements. Blood oxygen levels. Once upon a time these measurements were usually only taken at a hospital or clinic, but with the rapid adoption of smartphones and smartwatches, this data has become widely available with the touch of a button. The ubiquity of these tools has made it easier than ever to capture long-term data about a person’s health, and doctors, researchers and tech companies are all taking notice.

Jessilyn Dunn

One such researcher is Jessilyn Dunn, an assistant professor of biomedical engineering and biostatistics & bioinformatics at Duke University. As the director of the BIG IDEAs Lab (Biomedical Informatics Group: Integrating Data Engineering and Analytics), Dunn and her team study how digital biomarkers from wearable devices can help generate an overall picture of someone’s health. Their goal is to use these markers to identify health events like acute infections of diseases like COVID-19 and the flu, to more long-term problems like heart disease and diabetes.

“Our hope is that wearable devices can fill a gap in the health care world,” said Dunn, “For a lot of diseases, wearables data shows that something was happening subtly for a longer period of time before an event like a heart attack occurs. We want to use the data from these tools and pair it with clinical information to detect when someone may be at risk before serious events happen.”

And the amount of data used to make these kinds of insights is ever-growing.

As of 2024, nearly 31 percent of the general population of the U.S. owned a smartwatch. This widespread adoption meant that––for the first time––it was possible for researchers to gather large amounts of physiological and activity data from study participants as they go about their daily lives, rather than relying on self-reported data or data collected in a laboratory setting.

“Getting this kind of ‘real-world’ data can provide a more accurate and detailed picture of people’s typical physiology and habits, and how they respond to medical interventions,” said Dunn. “Data collected from these devices could have the potential to revolutionize many aspects of patient care, including outpatient care, clinical trials, and long-term health monitoring.”

Getting this kind of ‘real-world’ data can provide a more accurate and detailed picture of people’s typical physiology and habits, and how they respond to medical interventions. Data collected from these devices could have the potential to revolutionize many aspects of patient care, including outpatient care, clinical trials, and long-term health monitoring.

Jessilyn Dunn Assistant Professor of Biomedical Engineering

Recognizing their potential, digital health researchers have also started changing study designs to rely on participants using their own wearable devices rather than use tools provided by the researcher or hospital. These bring-your-own-device studies drastically increased after the COVID-19 pandemic, as researchers sped up efforts to detect illness early, provide medical care and conduct clinical trials remotely, improve resource allocation, and prevent further spread by leveraging data from individuals’ personally owned devices.

According to Dunn, the use of digital health tools in general health care has also exploded, with a greater number of health care providers showing interest in using wearable tools for patient care. For example, data from wearables has been collected to provide additional insight into patients’ physiological responses during clinical trials and are now being considered more seriously for use in endpoints by regulatory agencies like the US FDA. The long-term monitoring capabilities of wearables has even been highlighted in medical television shows. In one episode of The Pitt, physicians checked data from a patient’s watch to determine how long his heart rate had been elevated before he arrived at the emergency room.

“Wearables are a non-invasive, low cost, and accessible tool that could help us control the spread of harmful diseases,” said Dunn. “These devices could help arm health care professionals with the information they need to intervene early and deliver the right treatment to the right person at the right time.”

But as more people wear smartwatches and gather data about their own health, questions about the security of that personal information are also becoming more common.

Is Your Watch Watching You?

In 2018, the U.S. Military Central Command was forced to reassess its privacy policy for troops after workout routes were publicly uploaded to Strava, a social network for athletes. Reporters and researchers quickly realized that the location data uploaded from smartphones and smartwatches identified U.S. military bases and patrol routes in Afghanistan and Syria.

While many of these locations had already been identified in articles and other public findings, the larger concern from a security standpoint was the ability to use this data to identify individuals who had traveled those routes and track them to other military locations around the globe.

This incident wasn’t the result of a hack, but it dramatically illustrated how user data provided by smartwatches and smartphones could be used for unintended purposes.

A screenshot from Strava showing a ‘heatmap’ of the running routes of users around Duke University. More common running routes appear brighter and show different pathways around campus.

“One of the privacy questions we typically get from study participants involves whether we collect GPS data from their devices,” said Dunn. “We typically do not collect location data to reduce risk. With studies that do require location data as a part of the analysis, we will abstract the data to reduce risk”. One such example is an ongoing project on opioid use disorder, in which Dunn and her team take additional precautions with the sensitive wearable data by recoding patients’ location information (from exact GPS location to a label of high– or low-risk) before it lands on their servers so it can’t be reconstructed under any circumstance.

While researchers need to follow guidelines set by their IRB and/or funding agencies about how data is used, stored, and deleted, privacy practices vary depending on the company.

In a 2025 study published in Nature Digital Medicine, researchers from the University College Dublin in Ireland reviewed and ranked the privacy policies of 17 leading wearable technology manufacturers, including Apple, Google, Oura and Garmin, and assessed their standard privacy practices.

The researchers found that a large portion of companies failed to provide clear reports regarding how they shared user data with governments and third-party applications or organizations, and they often didn’t clarify why user information was shared. Most companies also lacked clear breach notification processes, which resulted in increased data security risk and slowed recovery response.

The study identified Google and Apple as the leaders in privacy protections, but even these industry-leaders have checkered histories with data security. In 2025, Apple settled a class-action lawsuit after it was revealed the Siri voice assistant was recording conversations on the Apple Watch via accidental activations. Google also agreed to pay nearly $400 million in a settlement in 2022 after investigations showed the company continued tracking Fitbit user location data after users had turned off location tracking.

Tracking Cycles and Signals

When asked about the knowledge gap between men’s and women’s health, Benjamin Smarr, an associate professor in the department of bioengineering and the Halicioǧlu Data Science Institute at the University of California San Diego, brings up heart attacks.

Most people know to connect left arm pain with a heart attack, especially when someone is suffering from chest pain and shortness of breath. What they don’t know, is that these symptoms typically only occur in men.

“Women don’t present the same way if they are suffering from a heart attack,” said Smarr. “Instead, they’ll often have dizziness, heartburn, and, most significantly, nausea or vomiting. Women have been suffering from heart attacks for thousands of years, but somehow, we only learned about this difference in the last decade. The truth is, we don’t know as much about women’s health because we’ve historically studied men.”

Like Dunn, Smarr and his lab use biometric data and wearable devices to identify trends and make practical insights that can be used to better understand physiology and overall health. One of the lab’s many projects involves collecting data from apps and wearables to learn more about women-specific health issues.

According to Smarr, the lack of historical knowledge surrounding women’s health means that there is a fairly low bar for progress. He believes wearables can help provide useful insights to begin to fill in these pervasive knowledge gaps.

Professor Benjamin Smarr

One of the team’s main projects explores how physiology changes across pregnancy. After a woman finds out she’s pregnant, she’ll typically go to an obstetrician to confirm the pregnancy and get an initial check-up. But after that first visit, patients are typically only seen for surface-level check-ups once every four weeks, with a few ultrasounds and more frequent appointments only in the late third trimester.

“When women visit the clinic throughout their pregnancies, their measurements and metrics are being compared against a textbook average rather than their own baseline,” said Smarr. “But every night of sleep, every heartbeat, every change in temperature––these measurements are personal, and personal trends may be very different than a global average.”

If the long-term monitoring of wearable devices can help determine that individual’s baseline, Smarr says, then it gives women and their doctors a much more personalized and useful understanding of how they are adapting to pregnancy.

One of the key measurements Smarr and his team use to decipher trends in women’s physiology is temperature––a metric that almost all smartwatches and wearables are now capable of providing. A women’s basal body temperature (BBT), which is the lowest body temperature recorded after at least six hours of uninterrupted rest, can be used to track a women’s menstrual cycle, as their temperature will rise when they ovulate and drop just before their period.

Smarr and his team have shown how to track these temperature changes to identify both early pregnancies as well as early miscarriages in their datasets.

“When someone gets pregnant, we’d see their temperature rise, and we’d then see it fall in a similar way to how it would before they’d menstruate, which indicates when a pregnancy is in danger or has already ended,” Smarr said. “Because these data are being taken continuously, these signals could encourage someone to take a pregnancy test and stop risky behaviors like drinking, and we could help inform someone to visit a hospital when a pregnancy is in danger or has already ended.”

While Smarr is optimistic about the opportunities wearable tools provide to improve women’s health, he also recognizes that changing political landscapes affect women’s willingness to share details about their cycles and pregnancies. This was especially clear after the 2022 Supreme Court case Dobbs v Jackson Women’s Health Organization, which eliminated the constitutional right to abortion in the U.S. and led to criminalization of abortion in some areas of the US.

Although Smarr says many women were still willing to share their data with his team, his lab also received lots of questions from people worrying about what could happen if their data were shared. For example, could someone subpoena their Fitbit to determine if they’d had an abortion? Smarr says concern and caution for participants shape what is group feels is ethical to publish.

“It really illustrates the bigger concerns about data ownership when it comes to wearables. When you upload data to your device, the company will often own that data,” he said. “And you don’t know if that company will decide to sell your data to a third party who could hand it over to the government. It creates a lot of unfair vulnerabilities.”

The issue puts women’s health between a rock and a hard place. On one hand, these tools could provide unprecedented insight for women who remain underserved in the medical world. But changing laws and threats of prosecution make sharing that intimate data potentially dangerous.

“It’s a sad reality, because you’re training people not to want to be more aware of their bodies and their health,” said Smarr. “We want to look where the light is, and the more data that’s available, the more we can use that to identify useful biomarkers. But these vulnerabilities are slowing the rate at which we can actually learn and use this data to help women.”

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