Apple has introduced an SOS button for the Apple Watch at WWDC.
WatchOS 3 has the ability for users to long press the side button to start a call with emergency services. After holding the side button, a countdown starts, a call beings, and users are able to talk with emergency services. Apple Watch also knows which country you are in and will be able to dial the correct number.
Apple Watch will also send a message to the emergency contact with a map of your location once the call has been finished. It will then display all the medical details of the user, which is entered in the Health app. HealthKit-enabled apps can also provide data for your medical details. Just in case the user is unconscious medical services will have info they need.