Outdoor Warning Sirens

Outdoor Warning Sirens

Outdoor Siren against cloudy blue sky background

Guidelines for the Activation of Outdoor Warning Systems

For Vermilion County Communities Effective April 10, 2010


The purpose of this document is to provide guidance to Vermilion County municipalities for the activation of community outdoor warning systems. This guidance is not a policy statement, but is presented to serve as a foundation on which a common approach can be used to provide warning of impending danger to county residents.

Legal Basis for Warning

The issuance of warning, and the approved signals that are used to convey that warning, as well as the procedures used to test those systems, are based on authority provided by Federal and State law and supporting guidance documents.

Pursuant to the provisions of the Federal Civil Defense Act (Public Law 81-920), which is the basis for the Civil Defense – or as we now call it “Emergency Management” program – Civil Defense is defined as:

…those activities and measures designed or undertaken (1) to minimize the effects upon the civilian population caused or which would be caused by an attack upon the United States or by a natural disaster, (2) to deal with the immediate emergency conditions which would be created by any such attack or natural disaster, and (3) to effectuate emergency repairs to, or the emergency restoration of, vital utilities and facilities destroyed or damaged by any such attack or natural disaster. Such term shall include, but shall not be limited to, (A) measures to be taken in preparation for anticipated attack or natural disaster (including… the provision of suitable warning system).

This statement charges federal, state, and local agencies with developing and maintaining the capability of warning the civilian population of impending disasters. This definition and statement is further described in the FEMA document CPG (Civil Preparedness Guide) 1-5. This document, entitled “Objectives for Local Emergency Management”, is the federal foundation that outlines the key elements of a local emergency management program.

CPG 1-5, Objective D (Alerting and Warning) clearly state that:

“The objective is to develop and maintain a capability to alert public officials and emergency response personnel and warn the general public of an actual or impending emergency.”

While the reference above relates to federal law, the Illinois Emergency Management Act (Public Act 85-168) further clarifies and assigns these responsibilities to units of local government. The EMA Act defines Emergency Services as:

“…the coordination of such functions by the State and its political subdivision, other than functions for which military forces are primarily responsible, as may be necessary and proper to prevent, minimize, repair, and alleviate injury and damage resulting from any natural or technological causes. These functions include, without limitation, … warning services, communication, … together with all other activities necessary or incidental to protecting life or property.”

Providing effective warning is accomplished by a variety of warning systems, which emanate from the Federal government level and ultimately rest on a local level.

Local Warning Systems

The local government portion of the warning system includes local government controlled warning and / or communications systems that are used for fan-out of warning and emergency information to local government officials, the general public, schools, and institutions which are within the government’s area of responsibility. These systems include outdoor and indoor warning systems supported by the Emergency Alert System (EAS).

The outdoor warning system includes: sirens, whistles, horns, and public address systems that are used to warn residents who are outdoors when a warning is given.

Standardized warning signals, for outdoor warning devices, have been established by FEMA. These standardized signals are used to alert the public and indicate survival action to be taken in an emergency.

These signals are ATTACK WARNING and the ALERT WARNING signals.


An ATTACK WARNING is a 3 to 5 minute wavering tone or siren, or a series of short blasts on horns or other devices. The ATTACK WARNING signal means that an actual attack or detected missile launch against the United States has been detected and that protective action should be taken immediately. The ATTACK WARNING shall be repeated as often as deemed necessary by local government authorities to obtain the required response by the population, including taking protective action related to the arrival of fallout.” Per federal guidance, “This signal will be used for no other purpose and will have no other meaning.”


An ATTENTION or ALERT WARNING signal is a 3 to 5 minute steady signal from sirens, horns, or other devices. This signal may be used as authorized by local government officials to alert the public of peacetime emergencies. In addition to any other meaning or requirement for action as determined by local government officials, the ATTENTION or ALERT signal shall indicate to all persons… “turn on your radio or television and listen for essential emergency information.”

The indoor warning systems are necessary for a well-balanced warning system. Outdoor warning systems may not be effective for warning in air conditioned buildings and it is not economical to use such devices in areas of low density population. Indoors warning systems include: commercial broadcast radio and television stations, cable television override systems, tone activated radio receivers, and public address systems.

The EAS, as a component of the indoor warning system, provides a means for local government to provide timely emergency warning and instructions to residents through the use of commercial radio and television. The EAS should be activated whenever a warning is disseminated to provide specific warning information.

Systems Test

It is especially important that local warning systems be tested on a periodic basis to be certain that they are operating properly and to help the public learn to recognize the warning signals.

Frequency of Tests

FEMA recommends regularly scheduled tests of warning systems accompanied by advance publicity to inform the public of the tests. FEMA also recommends testing once a month, at a minimum.

The Illinois Emergency Management Act of 1992 specifically indicates,

“… the testing of disaster warning devices, including outdoor warning sirens, shall be held only on the first Tuesday of each month at 10 o’clock in the morning or during disaster training exercises that are specifically and expressly approved in advance by the Illinois Emergency Management Agency.”

Activation of the countywide EAS should also occur as part of these regular monthly warning tests. The purpose of this activation is to educate county residents of the association between outdoor warning sirens and the EAS.

Test Procedures

Federal guidance indicates that monthly warning system test should occur in the following manner.

“The ATTENTION or ALERT signal should be sounded for 1 minute. This should be followed by 1 minute of silence, followed by the ATTACK WARNING signal sounding for 1 minute.”

This testing procedure will establish a test exercise pattern different from that used in an actual emergency. In an actual emergency, the ATTENTION I ALERT or the ATTACK WARNING signal will be sounded for 3 to 5 minutes.

Emergency Activation of Warning Systems for Severe Weather

Activation Criteria

During a severe weather incident, local warning systems should be activated if:

  • A tornado, funnel cloud aloft, potential for large hail, or high winds capable of causing considerable damage or death to persons is reported or detected approaching the community.
  • A confirmed sighting of a tornado, or funnel cloud aloft, reported by a trained municipal employee or trained Vermilion County Emergency Management Weather Spotter.
  • Advice from the National Weather Service.

A confirmed sighting is defined as a sighting that is observed either by a trained municipal or county employee, a trained Emergency Management Weather Spotter or Doppler radar indication.

An unconfirmed sighting is a report that is received from one or more members of the general public.

When an unconfirmed sighting is reported, a radio equipped municipal vehicle should be dispatched to investigate an unconfirmed report, and determine whether that report is valid or not. Confirmation of the sighting will result in a confirmed sighting report issued by the governmental employee.

Activation Area

Vermilion County has the capability of activating outdoor warning sirens county wide or in specific areas and regions. During severe weather it may be determined that just specific areas should be activated due to the nature and makeup of the approaching storm.

Activation Procedure

Following the occurrence of a weather event, meeting the above criteria, the Vermilion County Emergency Management Agency should activate the outdoor warning system and the Emergency Alert System.

Once activated, the warning system should not be re-sounded for the same storm or sighting.

The warning system should be re-sounded for any new confirmed siqhtinq that meets the activation criteria described above.

“All Clear” Procedure

In keeping with the policy of the National Weather Service, local government should not issue an “all clear” statement nor should they sound an all clear warning siren.

Severe Thunderstorm or Tornado watches, are traditionally issued for a period of six hours. The Weather Service may terminate a “watch” early if weather conditions change and the threat of severe weather no longer exist.

Severe Thunderstorm or Tornado warnings are traditionally issued for a period of one hour. Weather warnings are usually allowed to expire within the issued time period without early termination by the Weather Service.

Residents requesting “all clear” information should be advised to monitor commercial radio and television for further weather information, but local government should not issue an “all clear” statement.

No activation of outdoor warning signal should be used to signify the “watch” termination or any kind of “all clear” advisory.


  • Public Law 81-920
  • Public Act 85-168
  • FEMA CPG 1-5
  • FEMA CPG 1-14
  • FEMA CPG 1-17
  • “The Federal Civil Defense Act of 1950. as amended”
  • “The Illinois Emergency Management Act of 1992”
  • “Objectives for Local Emergency Management”
  • “Principles of Warning and Criteria Governing Eligibility for National Warning Systems Service”
  • “Outdoor Warning Systems Guide”