Hamilton County Emergency Management sounds the sirens when a tornado warning is issued by the National Weather Service or when a funnel cloud or tornado is sighted by a trained weather spotter or public safety. Sirens are grouped by municipality and the sirens for the municipality are sounded when a warning polygon incorporates the municipality. The only time Hamilton County Emergency Management activates all sirens is if a tornado warning polygon included the entire county. There is only the activation tone of the sirens; we do not use an all clear sound.
Sirens could potentially be used to alert people of a shelter in place or evacuation order; however, this would be done at the municipality level.
Sirens were first installed by Civil Defense as air raid sirens to warn the public of a possible attach or nuclear war. Civil Defense eventually transitioned to Emergency Management when sirens were then used for tornado warning. As communities have expanded, so have the sirens.
Hamilton County Emergency Management tests all sirens on Fridays at 11:00 a.m. The sirens are automatically sounded and a report is sent to several individuals. The report is reviewed for any issues. If maintenance is required, the municipality will contact their service provider to fix the sirens.
The system continuously checks the sirens to ensure they are in working order. For example, if the power goes out at a siren site, a message is sent to the system administrators. The system checks for communications, battery status, and many other settings.