(CNN) - A new study shows Apple Watches may be able to save lives by their ability to detect irregular heart rates.
Researchers looked at pulse data collected by the watch's heart rate monitor from 400,000 participants.
They sent electrocardiogram patches to wearers who showed irregular pulses.
About a third of them turned out to have atrial fibrillation, a potentially fatal condition that contributes to 130,000 deaths in the U.S. each year.
Researchers say false positives are a concern in these types of tests, and the Apple Watch returned those about 29 percent of the time.
The data collected for the study used simple pulse information because the version of the Apple Watch with ECG functionality had not been released yet when it began.
Scientists say the study shows potential, but note the results are preliminary.