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.

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.”

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.

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.

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.”