Current testing for coronavirus generally involves waiting until someone is sick before getting them tested and then trying to isolate them afterward if their test is positive. If we could easily identify people who are infected before they start showing symptoms, we’d be able to contain and treat them more effectively — and this may be possible using wearable health devices like the Apple Watch.

A study by researchers at New York’s Mount Sinai hospital, reported by CBS, shows how Apple Watches could spot a coronavirus infection before a diagnosis.

The researchers used data from Apple Watches to track a metric called HRV, or heart rate variability, which measures how much the time between a person’s heartbeats changes throughout the day. High HRV means that the person’s nervous system is responding to cues in a healthy and active way, while a low HRV implies that the nervous system could be struggling to adapt to changes. Scientists know that low HRV can predict if a person may be infected by a virus, so the researchers wanted to check whether it could be used to predict coronavirus infections in particular.

The researchers measured HRV from nearly 300 healthcare workers in the Mount Sinai Health System who volunteered to wear an Apple Watch and who download a special app for tracking their HRV. Of these healthcare workers who did catch coronavirus, the researchers found that changes in HRV occurred seven days before a positive coronavirus test was performed.

This means that changes in HRV as measured through a device like an Apple Watch could be used to identify coronavirus infections even before people realize that they are sick.

“Advances in digital health provide a unique opportunity to enhance disease containment,” the authors write, pointing out that people are already familiar with wearables like the Apple Watch for health monitoring, and that they have the advantage of not needing people to do anything active in order for data to be collected on them. This is compared to other options like using an app to track vital signs, which can be time-consuming and people can easily forget to do.

The paper has not yet been peer-reviewed, which means it has not yet been scrutinized by the medical community and its findings should be considered speculative. But it does point to a way that wearables like the Apple Watch could help with the identification, tracking, or monitoring of diseases like the coronavirus in the future.

A pre-print version of the paper is available on medRxiv.