The device, made by AliveCor, pairs the ability to take a personal 30 second electrocardiogram (EKG) with a feature that uses artificial intelligence to continuously evaluate the correlation between heart and physical activity. When the device, known as KardiaBand, detects that a user's heart rate and activity are out of sync, it prompts the user to capture an EKG by touching the band. The results display instantly on the watch face. The device is designed to capture information that can help doctors help manage atrial fibrillation, the most common heart arrhythmia that is a leading cause of stroke and affects more than 30 million people worldwide. The device costs $199 and requires a subscription to the company's premium service for $99 a year.