Building on previous disaster response efforts, Twitter is rolling out a feature that will let agencies broadcast messages in a crisis. The program, called simply Twitter Alerts, lets users sign up for emergency messages from agencies like FEMA, the World Health Organization, and local police departments. Once you opt into an individual organization's alerts, it can send you push notifications and text messages in case of an emergency, like a less formal version of the severe weather warnings the National Weather Service sends straight to smartphones. When you open your Twitter feed, those alerts will also be highlighted in the stream.

Twitter has previously partnered with local governments in Japan to offer disaster information, but this is something much more proactive — and potentially annoying or dangerous. Anyone can sign up to receive alerts, but for now, Twitter is carefully curating who can send them. A current list of organizations includes several US city police or fire departments, nationwide agencies like the State Department and the Department of Homeland Security, and disaster services in Korea and Japan, as well as some international organizations.

These agencies, as well as potential future applicants, are strictly admonished not to inundate users with unnecessary alerts, providing only vital crisis updates. "Twitter Alerts should not be used for general updates about your organization," it writes, and tweeting fundraising requests or anything commercial is strictly forbidden. Attempting to head off mass alerts by the Syrian Electronic Army, Twitter is also requiring any participating organization to "increase the security" of its Twitter account before using the system.

It's not absolutely clear, but it appears that alerts are broadcast to all subscribers, regardless of location. Since it's an opt-in procedure, though, users should be able to pick the local organizations that best apply, and alerts for a specific group can be turned off at any time. While texts and push notifications should be limited, approved organizations can post as many normal tweets as they want without running up against Twitter's spam limits. Twitter is quick to say that this program isn't a substitute for traditional communication channels, but given that agencies are already using it to disseminate information, an official alert system is a thoughtful change.