For Facebook on iOS, Safety Check automatically sends users a Facebook push notification if they are in the area of a disaster and prompts them to answer if they're safe. From there, users can select an "I'm Safe" option which will automatically generate a notification and a story in the News Feed. Friends that are marked safe will also show up in the News Feed with a list of their most recent updates.
To determine your location, Facebook looks at the city listed on your profile and recognizes the city where internet services are being used. The company will also use data from the Nearby Friends feature if a user has turned it on. Safety Check's sign-in feature is similar in nature to the Safe and Well website created by the American Red Cross which also allows individuals to register themselves as safe and inform their loved ones of their current conditions.
Facebook's new Safety Check feature comes after the company launched an update to its iOS app yesterday that added support for the iPhone 6 and the iPhone 6 Plus. Facebook for iOS is a free app and can be downloaded from the App Store. [Direct Link]