Types of Tornado Sirens

Understanding the uses of Civil Defense sirens in the United States is a helpful way of ensuring a proper response to warnings and alerts, including tornadoes. While there are no sirens exclusively used for tornadoes, general alerts are signaled warning the public to head indoors and check the Public Alert Broadcast System through radio and television interruptions that communicate the cause of the siren alert.

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Distinguishing Sirens
- Civil Defense sirens generally have two types of signals, the attention or alert signal and the attack warning. The alert signal consists of a three- to five-minute steady tone, generally beginning quietly and rising in volume over time before again receding. Alert signals are used in the cases tornadoes, floods and other weather-related issues. A short series of blasts or a wavering tone is an attack warning. This involves wartime concerns such as air raids. Occasionally, high and low tones akin to those of emergency vehicles may be heard in cities or towns connected with fire departments.
Siren Testing
- Civil Defense sirens may regularly be tested weekly, monthly or yearly. In some towns or cities they are also used to announce intervals of the day, such as a noon siren or a 5 p.m. one.
History
- Sirens were not heavily used in the early 1900s, but they became common during World War II as a response to the threat of foreign air raids or invasion. In the post-war years they were extended to weather issues and nuclear emergencies in response to the development of the Cold War.
Public Concern
- Civic alert sirens are generally run on a local governmental level. Because they were originally intended to warn people outdoors to seek shelter, warning systems may be inadequate to reaching individuals who are indoors, especially if the warning is issued late at night. A commonly recommended alternative is to always keep a storm weather radio to check for weather alert warnings.