Terror alert system

Terror alert systems are standardized frameworks employed by governments to communicate the assessed likelihood and potential severity of terrorist threats, enabling authorities, organizations, and the public to take appropriate preventive measures. These systems typically employ tiered threat levels, ranging from low to critical, and are designed to reflect each country’s specific security context, intelligence assessments, and risk management strategies. They provide guidance on protective measures, situational awareness, and coordinated responses across federal, regional, and local agencies.

Terror alert systems are an integral part of national security strategies, aiming to enhance public safety through timely communication, clear guidance, and preparedness planning. Examples include the United States’ National Terrorism Advisory System (NTAS), the former Homeland Security Advisory System (HSAS), the United Kingdom’s UK Threat Levels, Canada’s National Terrorism Threat Level (NTTL), and the Netherlands' Counterterrorism Alert System and Terrorist Threat Assessment Netherlands (DTN).

Australia

National Counter-Terrorism Alert Level

• Certain - terrorist attack is imminent or has occurred
• Expected- terrorist attack is highly likely
• Probable - terrorist attack is likely
• Possible - terrorist attack could occur
• Low - terrorist attack is not expected

Administered by the Federal Attorney-General's Department.

Canada

Canada's National Terrorism Threat Level (NTTL) is a federal tool indicating the likelihood of a violent terrorist act occurring in Canada. It is assessed by the Integrated Terrorism Assessment Centre (ITAC) and approved by the Director of the Canadian Security Intelligence Service (CSIS). ^[1] ITAC considers classified intelligence and open-source intelligence on the intentions, capabilities, and opportunities of terrorist actors when making its assessment. Its purpose is to ensure a shared understanding of national risk and to guide appropriate responses across government and law enforcement. When the threat level rises to High or Critical, the Federal Terrorism Response Plan may be activated, coordinating emergency measures across federal, provincial, and territorial authorities. ^[2]

National Terrorism Threat Level ^[3]

• Very low - A violent act of terrorism is highly unlikely. Measures are in place to keep Canadians safe.
• Low - A violent act of terrorism is possible but unlikely. Measures are in place to keep Canadians safe.
• Medium - A violent act of terrorism could occur. Additional measures are in place to keep Canadians safe.
• High - A violent act of terrorism is likely. Heightened measures are in place; Canadians are informed what actions to take.
• Critical - A violent act of terrorism is highly likely and could occur imminently. Exceptional measures are in place; Canadians are informed what actions to take.

Canada's current level is Medium, a level that has been in effect since October 2014. ^[3] Threat levels are assessed at a minimum of every four months, or more frequently as required. ^[3]

France

Main article: Vigipirate

Plan Vigipirate

• Yellow - to stress vigilance
• Orange - to warn of terrorist action
• Red - to warn of serious attempts
• Crimson - to warn of major attempts

Ireland (Republic of)

International Terror Threat Level

• Low: An attack is deemed unlikely.
• Moderate: An attack is possible, but not likely.
• Substantial: An attack is a strong possibility.
• Severe: An attack is highly likely.
• Critical: An attack is imminent or has occurred.

Administered by the Garda Síochána. ^[4]

Since November 2015, the international terrorism threat level is considered to be at moderate, meaning an attack is "possible but not likely". ^{[5] [6]}

Netherlands

Main article: Nationaal Coördinator Terrorismebestrijding en Veiligheid

Russia

• Blue - an unconfirmed information about real terroristic threat ^[7]
• Yellow - a confirmed information about real terroristic threat
• Red - an information about committed terrorist act

United Kingdom

Main article: UK Threat Levels

The United Kingdom’s terrorism threat level system is maintained by MI5 and the Joint Terrorism Analysis Centre (JTAC) to communicate the likelihood of a terrorist attack. ^[8] It categorizes threats into five levels: Low, Moderate, Substantial, Severe, and Critical, reflecting increasing probability of an attack. ^[8] These levels are determined through intelligence assessments and are intended to guide protective security measures across government, businesses, and public sectors. ^[8] Changes to the threat level are publicly announced to inform the public while ensuring appropriate security measures are implemented nationwide. ^[8]

Terrorism Threat Levels ^[8]

• LOW - an attack is unlikely
• MODERATE - an attack is possible, but not likely
• SUBSTANTIAL - an attack is likely
• SEVERE - an attack is highly likely
• CRITICAL - an attack is highly likely in the near future

The UK's (England, Wales, Scotland and Northern Ireland) current level is SUBSTANTIAL, ^[8] while Northern Ireland's current level is SUBSTANTIAL. ^[8]

United States

Homeland Security Advisory System

Main article: Terror Alert Level

• Low - Low risk of terrorist attacks
• Guarded - General risk of terrorist attacks
• Elevated - Significant risk of terrorist attacks
• High - High risk of terrorist attacks
• Severe - Severe risk of terrorist attacks

Administered by the Department of Homeland Security

National Terrorism Advisory System

• Elevated Threat - Significant or high risk of terrorist attacks
• Imminent Threat - Critical risk of terrorist attacks

References

1. "National Terrorism Threat Level – Questions and Answers". Public Safety Canada. Retrieved 7 September 2025.
2. "Federal Terrorism Response Plan" (PDF). Public Safety Canada. 2013. Retrieved 7 September 2025.
3. "Canada's National Terrorism Threat Level". Public Safety Canada. Retrieved 7 September 2025.
4. O'Keeffe, Cormac (2 May 2016). "What is the reality of the threat posed by Islamic extremists in Ireland?". Irish Examiner. Archived from the original on 3 May 2016. Retrieved 11 May 2016.
5. "Terror threat level unaffected by attacks". Irish Independent. 27 June 2015. Archived from the original on 25 September 2015. Retrieved 1 July 2015.
6. Williams, Paul; Brady, Tom (24 November 2015). "Units to counter terrorism step up training". Irish Independent. Archived from the original on 25 November 2015. Retrieved 24 November 2015.
7. УРОВНИ ТЕРРОРИСТИЧЕСКОЙ ОПАСНОСТИ | Национальный антитеррористический комитет (in Russian)
8. MI5. "Terrorism threat levels." MI5. Accessed September 7, 2025. (https://www.mi5.gov.uk/threats-and-advice/terrorism-threat-levels)