The iPhone has always had the option to dial an emergency number without a passcode or activated service, but this feature has been improved exponentially in iOS 8. New emergency call features are integrated with the new Health app that was released with iOS 8. Though the app is targeted at younger, more health conscious individuals, the Health app is there to provide assistance to those that have serious medical conditions too.
Now when someone tries to use your phone in an emergency, but cannot unlock the phone. They can tap "Emergency" in the bottom left corner of the device's screen. This will show the traditional keypad for dialing emergency numbers only, but also a new area appears in the bottom left corner called "Medical ID."
Medical ID, when tapped, will show everything you have told the Health app on iOS 8 about your current medical conditions. The app can list your diet, allergies, and most importantly, emergency contacts other than the obvious 911. The emergency contacts have telephone icons next to the names of the listed individuals so when someone taps the icon it will dial the number for the corresponding contact. This way your loved ones can be reached faster even if you are not able to unlock your phone for the good samaritan who may help you in an emergency.