Outdoor Warning Siren System

What is the Purpose of the Sirens?

Hamilton County’s Outdoor Warning Siren System consists of approximately 190 strategically-placed sirens. These sirens serve as an early warning device to alert citizens to take shelter indoors and seek additional information. While the outdoor warning system can be an effective method of notifying those that are outdoors, to seek shelter indoors, it is only one component of a comprehensive emergency warning system. In addition, you should obtain a NOAA weather radio and tune in to local media reports from television, radio, or social media.
FederalDesigned as an Outdoor Warning System, the sirens SHOULD NOT be relied upon to provide sufficient warning INDOORS or in NOISY AREAS. Additionally, air conditioning, thunder, wind, rain, and other conditions can cause the sirens not to be heard indoors or outdoors, even if sirens can be heard during monthly tests.  Sirens are also subject to lightning strikes and other equipment malfunction.  Because the sirens are constantly exposed to the elements and other hazards, Hamilton County EMHSA cannot guarantee that the sirens will function correctly. For these reasons, everyone is encouraged to have multiple ways to receive information about severe weather.

Activation Criteria

There are three basic criteria that Hamilton County EMHSA uses to activate the sirens:

  1. The National Weather Service (NWS) issues a Tornado Warning for Hamilton County.
  2. A tornado is reported by a local public safety official (police/firefighter) to the NWS or to Hamilton County EMHSA.
  3. A dangerous situation occurs which requires the public to seek shelter indoors immediately.

Hamilton County has the capability of activating all of the sirens at once or by activating one or more of six siren zones. All sirens are sounded unless the threat is clearly confined to an individual zone (or zones). During a tornado warning, the sirens will be sounded for a three minute duration in ten minute intervals (three minutes on, seven minutes off) for as long as the tornado warning is in effect. There is NO “all-clear” siren.

Siren Test Cancellation Criteria

Basic criteria for cancelling the activation of the Outdoor Warning Sirens include:

  1. Extreme cold, freezing rain/drizzle, and/or icing that may damage the equipment.
  2. Presence of severe weather (or potential severe weather) occurring in the local area, which may cause confusion as to whether the activation is a real event.

Monthly Testing:

The Outdoor Warning Siren System will be tested on the first Wednesday of each month at 12:00 p.m., unless there is inclement weather in Hamilton County. A siren test will consist of a single siren tone, lasting approximately 1 minute. Hamilton County EMHSA will notify the public via press release and social media posts when a siren test is planned, cancelled, or rescheduled, prior to the time at which the sirens will sound.

If Hamilton County is experiencing severe weather prior to 12:00 p.m. on a scheduled test day, the siren test may be postponed, to the determined alternate test day, which is the second Wednesday of the month, at 12 p.m. Testing for the alternate day will consist of a “Growl” test. A “growl” test is a quick sounding of the sirens, lasting approximately six seconds, which tests the activation and rotation of each siren. If testing the sirens on the alternate day is also canceled, the Outdoor Warning Siren tests will resume on the next scheduled monthly date.

Siren testing may be suspended during the winter months (December – February) when ice or sub-freezing temperatures could damage the siren system. If there is an emergency during winter months, the sirens will be activated to notify people of the need to seek shelter.

If testing is required at any time outside of the normal monthly testing schedule, Hamilton County Emergency Management and Homeland Security Agency will be sure to notify the public via social media posts and press release.

Siren Maintenance

Hamilton County EMHSA maintains approximately 190 sirens throughout the county. Each siren is inspected at least every three years. The maintenance/inspection program as adopted by Hamilton County EMHSA consists of checking the operations of the siren, battery strength, terminal connections, site conditions, obstructions that may interfere with the siren. During maintenance and inspection, the siren is “growled.” This short activation may occur several times during our inspection. If you have questions regarding a siren being sounded in your neighborhood, please feel free to contact Hamilton County EMHSA. The siren contractor hired by Hamilton County EMHSA to conduct maintenance on the sirens, is documented and will be carrying identifying information.

Outdoor Warning Siren System Informational Brochure