Outdoor Warning Sirens


Outdoor Warning Sirens (commonly called “tornado sirens”) may be the most instantly recognizable method of public warning currently in use. 

There are 136 warning sirens located within St Charles County. The majority of these units are powered by batteries charged by solar panels. The cost of installing a siren now ranges between $30,000 and $50,000. Seventy-three units were installed and are maintained by St. Charles County Regional Emergency Management, and the rest were installed and managed by local municipalities.  

Though nearly everyone has heard them, not everyone understands what they mean - especially because siren policies can differ from county to county. Understanding when, why, and how sirens are used in St Charles County can directly affect the safety of individuals and families when quick action is necessary.

> View a map of St. Charles County warning sirens.

Outdoor Alert Siren

For St. Charles County residents, St. Charles County Regional Emergency Management offers this list of Five Facts Emergency Managers Want You to Know About Outdoor Warning Sirens.

1. Warning sirens are activated when a tornado warning is issued or there is visual confirmation of a tornado in St. Charles County.

The goal for these warnings is to alert residents and visitors that a hazard exists and to signal the need to obtain further details about the situation. When residents hear a siren, they should:

  • Quickly observe conditions around them.
  • If there is a visible threat, immediately take cover in the safest structure available.
  • If there is no threat visible, go inside to a safe location and tune to broadcast media, NOAA Weather Radio, or internet for specific information about the danger.

2. Warning sirens aren’t designed to be heard indoors.

They are designed to warn anyone outside to move indoors to a safe place and to obtain further details about the situation. Even if sirens are normally audible inside the home, noise from wind, thunder, or hail can prevent occupants from hearing during severe weather. As a precaution, residents are strongly urged to have more than one source for emergency alerts and information inside the home.

3. St. Charles County does not automatically activate warning sirens whenever a warning is issued in an adjacent county.

St. Charles County policy is to activate sirens when a warning is issued for an area within the county. If a threat in an adjacent county is close enough, and moving toward the county line, Emergency Management may activate sirens to ensure our residents have time to act. That decision is made on a case-by-case basis.

4. When the sirens are activated, normally they are activated county-wide.

Sirens have been purchased over many years, from various manufacturers and by different jurisdictions. As the cities and county grew, the sirens have been linked to form the current siren network. With the current system, it has been determined that selecting and grouping the correct sirens for the specific area under warning would be slower and less efficient than activating the entire system that alerts our entire county. 

5. Warning sirens do not sound “all clear” signals.

If you hear sirens sound more than once, that means that another warning or danger to public safety exists. Please take precautions and obtain more information to protect yourself and others from this additional threat.


Warning sirens are tested regularly to ensure they will function properly in an emergency. So each month on the first Monday, sirens are run full strength for 3 minutes to make sure amplifiers and batteries maintain proper power through the full cycle. Additionally, sirens are tested silently each week. Silent tests can indicate that all components and batteries are functional, but don’t indicate how the power source will perform during full operation. 

Outside of these routine tests, sirens are also tested individually following routine maintenance or unscheduled repairs.

How to Report Malfunctioning Warning Sirens

Warning sirens can malfunction for a number of reasons. For example, they are frequently damaged by lightning. Surprisingly, another common cause of damage is by collisions with large vehicles and heavy equipment.

If you notice that a siren doesn’t appear to be working properly, don’t wait. Report it. Please contact St Charles County Regional Emergency Management at 636-949-3023. Emergency Management staff will notify the jurisdiction responsible for repairing the problem.