The Department of Homeland Security has in place a National Terrorism Advisory System (NTAS), a system to communicate effectively information about terrorist threats by providing timely, detailed information to the public, government agencies, first responders, airports and other transportation hubs, and the private sector.
Terrorism information, intelligence and threat level is based on the collection, analysis and reporting of a range of sources and methods. While intelligence may indicate that a threat is credible, specific details may still not be known. Alerts provide information to the public about the threat, including, if available, the geographic region and protective actions being taken by authorities, and steps that individuals and communities can take to protect themselves and their families, and help prevent, mitigate or respond to the threat.
The National Terrorism Advisory System contains three threat levels:
Imminent Threat Alert: Warns of a credible, specific and impending terrorist threat against the United States.
Elevated Threat Alert: Warns of a credible terrorist threat against the United States. After reviewing the available information, the Secretary of Homeland Security will decide, in coordination with other Federal entities, whether an NTAS Alert should be issued. NTAS Alerts will only be issued when credible information is available.
Sunset Provision: An individual threat alert is issued for a specific time period and then automatically expires. It may be extended if new information becomes available or the threat evolves.