You do not need a screen protector for the Apple Watch as it is scratch-resistant to a passable degree. However, you can always add one to give you added peace of mind. It will protect the watch against scratches and drops. However, if you are planning to use the watch for outdoor activities such as rock climbing, you should consider a case that will protect the watch against shocks and scratches. Not only this, you should buy a rugged case for the watch.