With the Apple Watch Series, you can keep track of your health and workouts as well as receive tips to improve them. You can also measure your sleep accurately and you can see if you have an irregular heart rate thanks to the ECG heart rate sensor. Thanks to the Always On display, you can see the time and notifications at a glance. You can view the various sizes watch cases in the store, so you're sure which Watch Series fits you well. Measure your wrist and choose the right size watch strap. With the Cellular models, you stay available even when your iPhone isn't near. You do need an eSIM phone plan for this.