Terror Alert Systems Fast Facts

(CNN)Here is a look at terror alert systems in the United States. In 2011, the US Department of Homeland Security (DHS) replaced the color-coded threat scale of the Homeland Security Advisory System (HSAS) with a new terror alert system, the National Terrorism Advisory System (NTAS). Also, Wireless Emergency Alerts (WEA), operated by the Federal Communications Commission (FCC), allow mobile phone users to receive targeted text messages about safety threats.

The National Terrorism Advisory System (NTAS) (2011-present):
April 26, 2011 -
The National Terrorism Advisory System (NTAS) replaces the color-coded Homeland Security Advisory System (HSAS).
When there is information about a threat, an NTAS Alert will simultaneously be posted on the National Terrorism Advisory System's website and released to the news media for distribution. The advisory will indicate whether the threat is "elevated," if there is no specific information about the timing or location, or "imminent," if the threat is impending or very soon. NTAS Alerts carry an expiration date and are automatically canceled on that date. If the threat information changes, the Secretary of Homeland Security may announce an updated NTAS Alert.
December 7, 2015 - DHS Secretary Jeh Johnson says his department will unveil a new national alert system in the coming days to reflect a "new phase" of the terror threat.
    December 16, 2015 - Johnson unveils a new intermediate advisory to the National Terrorism Advisory System, the NTAS "Bulletin." The first bulletin is issued and expires in six months.
    BULLETIN
    - Describes current developments or general trends regarding threats of terrorism.
    ELEVATED ALERT
    - Warns of a credible terrorism threat against the United States.
    IMMINENT ALERT
    - Warns of a credible, specific and impending terrorism threat against the United States.
    Wireless Emergency Alerts (WEA):
    2006 -
    Congress passes the Warning, Alert and Response Network (WARN) Act, requiring carriers that choose to participate to activate the technology by April 2012.
    May 10, 2011 - FCC Chairman Julius Genachowski, FEMA Administrator Craig Fugate, and New York City Mayor Michael Bloomberg unveil an alert system that will be available in New York City by the end of 2011 and eventually nationwide. It is originally called Personal Localized Alerting Network (PLAN) but its name later changes to WEA.
    - WEA allows government officials to send emergency alerts to all subscribers with WEA-capable devices if their wireless carrier participates in the program. Consumers do not need to sign up for this free service.
    - Consumers receive three types of alerts from WEA: alerts issued by the president, alerts involving imminent threats to safety and Amber Alerts. Subscribers can block all but presidential alerts.
    - AT&T, Sprint, T-Mobile, and Verizon are among participating carriers.
    Homeland Security Advisory System (HSAS) (2002-2011):
    March 12, 2002-April 25, 2011 - The Homeland Security Advisory System acts as a color-coded terrorism threat advisory scale. The level never goes below yellow.
    August 10, 2006 - The DHS raises the threat level for commercial flights originating in the United Kingdom bound for the US to red. Raises level to orange for all commercial aviation in or destined for the United States. Three days later the DHS lowers the threat level back to orange.
    RED - "Severe"
    Risk of terrorist attack: SEVERE
    - Assign emergency response personnel and pre-position emergency response teams.
    - Monitor, redirect or constrain transportation systems.
    - Close public and government facilities.
    - Increase or redirect personnel to address critical emergency needs.
    ORANGE - "High"
    Risk of terrorist attack: HIGH
    - Coordinate necessary security efforts with armed forces or law enforcement agencies.
    - Take additional precautions at public events.
    - Prepare to work at an alternate site or with a dispersed work force.
    - Restrict access to essential personnel only.
    YELLOW - "Elevated"
    Risk of terrorist attack: SIGNIFICANT
    - Increase surveillance of critical locations.
    - Coordinate emergency plans with nearby jurisdictions.
    - Assess further refinement of protective measures.
    - Implement contingency and emergency response plans as appropriate.
    BLUE - "Guarded"
    Risk of terrorist attack: GENERAL
    - Check communications with designated emergency response or command locations.
    - Review and update emergency response procedures.
    - Provide the public with necessary information.
    GREEN - "Low"
    Risk of terrorist attack: LOW
    - Refine and exercise preplanned protective measures.
    - Ensure that emergency personnel receive training on protective measures.
    - Regularly assess facilities for vulnerabilities and take measures to address them.