A smartwatch with a pulse sensor could easily detect an arrhythmic pulse, which can be a symptom of atrial fibrillation, one of the most common causes of stroke

A smartwatch with a pulse sensor could easily detect an arrhythmic pulse, which can be a symptom of atrial fibrillation, one of the most common causes of strokes. You couldn't diagnose a stroke itself just from heart rate and blood pressure, though. There's way too many other factors that can cause variations in those.