We know we’re living in the future. But it’s rare that we get actual hard data on whether a new technology we are inviting into our lives is a good idea. Such an opportunity will come Saturday, when we’ll learn more about the Apple Watch and its ability to detect serious heart conditions such as atrial fibrillation. Researchers from Stanford will present the results of a study of more than 400,000 patients testing the device’s ability to accurately detect heart rhythm problems, which can lead to strokes and other problems. The Apple-sponsored study will be the first test of whether putting wrist sensors on people to detect heart rhythm changes is a good idea that gets them the necessary care, or a bad one that is raising false alarms and possibly leading to overtreatment of the worried well. It is also one of the largest heart screening studies ever.