Sky Labs, a Korea-based digital health company, said its smart ring medical device CART-I outperformed the Apple Watch in detecting atrial fibrillation (AF) in a head-to-head clinical study conducted in the U.K.

The study results were recently published in the peer-reviewed journal Heart Rhythm O2.

The comparative clinical trial, involving approximately 500 patients, was carried out at three U.K. hospitals—Oxford, Southampton, and Birmingham. Researchers simultaneously evaluated the CART-I ring and Apple Watch under identical conditions.

Both devices rely on single-lead electrocardiogram (SL-ECG) data to detect AF using automatic algorithms. According to the study, CART-I achieved an AF detection sensitivity of 84.6 percent, higher than the Apple Watch’s 69.1 percent.

Although there was a difference in AF detection, both devices demonstrated strong performance in ECG interpretation. The Apple Watch showed a 95.4 percent sensitivity in SL-ECG analysis, while CART-I followed closely with 94.3 percent.

Notably, the study expanded its scope beyond AF to include a broader range of arrhythmias, such as atrial flutter and atrial tachycardia—an approach rarely taken in previous comparative studies.

However, the researchers noted that despite promising results, wearable devices alone are not yet sufficient for diagnosing complex arrhythmias like atrial flutter or tachycardia. They stressed the continued importance of physician-led interpretation, highlighting the role of automated algorithms as supplementary tools rather than standalone diagnostic systems.

“This study serves as international validation of CART-I’s atrial fibrillation detection capabilities,” Sky Labs CEO Lee Byung-hwan said. “Alongside our blood pressure-focused CART BP, these findings demonstrate the clinical potential of our technology across a broad range of cardiovascular conditions.”

The company will continue to develop medical devices that combine precision and ease of use for patients, Lee added.