The Apple Watch is already a wonderful health tracker. With the Alivecor KardiaBand, you can do more with it. This wearable EKG recorder replaces the standard Apple Watch band and detects irregular heart beat quickly. Its app has SmartRhythm monitoring that evaluates your heart rate and activity.
The bad news? You are going to need a premium app to take full advantage of this toy. The KardiaBand is available for 38mm and 42mm models.