WASHINGTON (AP) — A huge study suggests the Apple Watch can detect a worrisome irregular heartbeat at least sometimes — but experts say more work is needed to tell if using wearable technology to screen for heart problems really helps.

More than 419,000 Apple Watch users signed up for the unusual study, making it the largest ever to explore screening seemingly healthy people for atrial fibrillation, a condition that if untreated eventually can trigger strokes.

Stanford University researchers reported Saturday that the watch didn't panic flocks of people, warning just half a percent of particip...