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The original item was published from 3/3/2015 10:13:56 AM to 4/4/2015 12:05:01 AM.

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SCCMO General Press Releases

Posted on: March 3, 2015

[ARCHIVED] Outdoor Warning Sirens 101: How Alerts are Issued and Sent

March 3, 2015
Contact: Colene McEntee, Public Affairs Coordinator, 636-949-1864,

St. Charles County, Missouri – We often hear them on the first Monday of every month and pay special attention when forecasts call for threatening weather. Although most recognize that Outdoor Warning Sirens and other mass alerting systems warn us of potential dangers, there are several misconceptions.

Understanding how and why alerts are issued and sent is important. To help clarify how sirens are activated in St. Charles County, here are five things to know from the St. Charles County Division of Emergency Management:

1. Outdoor Warning Sirens are activated when a warning is issued by the National Weather Service or there is visual confirmation of the event in St. Charles County – The goal of these sirens is to alert citizens that a hazard exists. It signals that individuals should enact their response plans and seek further information for more details.

2. Outdoor Warning Sirens are not designed to be heard indoors – Although sirens may typically be audible within your building, they are intended to warn those outdoors to seek shelter indoors. When indoors, do not rely solely on Outdoor Warning Sirens to warn you of threats, as noise from the storm and other complications may prevent you from hearing them. For indoor use, it is recommended that homes and businesses use a battery-operated NOAA Weather Radio, alert applications, text alerts and other methods for information.

3. St. Charles County does not automatically activate Outdoor Warning Sirens whenever warnings are issued in adjacent counties – Operational policies differ throughout the country, but in St. Charles County, sirens alert for the entire population when a warning is issued within the county. If the threat is in an adjacent county and appears to move toward the county boundaries, the Division of Emergency Management may activate warning sirens to insure citizens have time to take refuge. This decision is made on a case-by-case basis.

4. When Outdoor Warning Sirens are activated within St. Charles County, they are typically activated county-wide – St. Charles County’s Division of Emergency Management activates the sirens for the entire county and serves as the backup for the City St. Peters, which activates its own sirens. With the current network used by St. Charles County, it is more efficient and faster to activate the entire system, as opposed to selecting and grouping by the area threatened. In addition to this efficiency factor, as tornadoes do not travel along set paths, this policy allows citizens a safer option, should the source of the danger change direction or spin up in multiple areas.

5. “All Clear” signals are never issued – If you happen to hear an Outdoor Warning Siren issued more than once during an event, this means that another warning or danger to public safety exists.

For more information on St. Charles County’s Division of Emergency Management and severe weather preparedness, visit


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