On 26 September, 2013, Twitter Announced the Following:
Today, we’re launching Twitter Alerts, a new feature that brings us one step closer to helping users get important and accurate information from credible organizations during emergencies, natural disasters or moments when other communications services aren’t accessible.
If you sign up to receive an account’s Twitter Alerts, you will receive a notification directly to your phone whenever that account marks a Tweet as an alert. Notifications are delivered via SMS, and if you use Twitter for iPhone or Twitter for Android, you’ll also receive a push notification*. Alerts also appear differently on your home timeline from regular Tweets; they will be indicated with an orange bell.
To subscribe to these notifications, you can go directly to an account’s setup page, which you’ll find at twitter.com/[username]/alerts. See FEMA’s page at twitter.com/FEMA/alerts for an example. Additionally, on web, you can see if an organization is part of the program when you visit its profile.