Alerts, Notifications, and Warnings

Denver ’s Outdoor Warning Sirens: What To Do When They Sound

The City and County of Denver has an outdoor warning siren system consisting of 86 electro-mechanical sirens (including nine at Denver International Airport). The sirens are tested on the second Wednesday of each month at 11:00 a.m.

Aside from the monthly tests, the siren system is only activated when a tornado has been spotted by trained observers, or when the National Weather Service has issued a Tornado Warning for Denver County .  A Tornado Warning means that a tornado has been sighted, or that a developing tornado is reported by trained spotters or indicated on Doppler radar. A warning is typically issued for a small area for less than an hour.  Denver ’s siren system can be activated for either the entire county or for specific affected areas.

Questions and Answers about the Denver Outdoor Warning Sirens(PDF, 655KB)

Alert and Warning Systems

Denver Outdoor Warning Sirens

When the sirens sound, you should seek shelter immediately:

If you are in: Then:

A structure (e.g. residence, small building, school, nursing home, hospital, factory, shopping center, high-rise building)

Go to a pre-designated shelter area such as a safe room, basement, storm cellar, or the lowest building level. If there is no basement, go to the center of an interior room on the lowest level (closet, interior hallway) away from corners, windows, doors, and outside walls. Put as many walls as possible between you and the outside. Get under a sturdy table and use your arms to protect your head and neck. Do not open windows.

A vehicle, trailer, or mobile home

Get out immediately and go to the lowest floor of a sturdy, nearby building or a storm shelter. Mobile homes, even if tied down, offer little protection from tornadoes.

Outside with no shelter

Lie flat in a nearby ditch or depression and cover your head with your hands.Be aware of the potential for flooding!

Do not get under an overpass or bridge. You are safer in a low, flat location.

Never try to outrun a tornado in urban or congested areas in a car or truck. Instead, leave the vehicle immediately for safe shelter.

Watch out for flying debris. Flying debris from tornadoes causes most fatalities and injuries.

Once you have reached shelter, you should tune into local news media for additional information. Denver’s sirens do not sound an “All Clear” tone, so consult the news media to learn when the danger has lifted. 

Emergency Alert System

The Emergency Alert System (EAS) is a national warning system that sends emergency messages to radio and television stations, to include cable and satellite stations. The system enables Federal, state and local governments to notify the public of emergency and disaster information. The system is also used to notify the public of severe weather alerts issued by the National Weather Service. The system can be used to send alerts by county or statewide. Radio Station 850 KOA (AM) is the designated primary EAS activation station for the Denver area; however, all local radio and TV stations typically broadcast EAS messages.

Radio and television stations are required to test the EAS weekly, however this weekly test may not include audio or video components. Audio and visual tests are conducted monthly.

NOAA Weather Radio

A National Oceanic and Atmospheric Administration (NOAA) Weather Radio is a dedicated radio that receives real-time weather information direct from the National Weather Service.  Routine weather messages are typically repeated every 4 to 6 minutes and are updated every 1 to 3 hours.  During severe weather, more frequent updates and live broadcasts are used to notify listeners of potential hail, flooding, tornadoes, blizzard conditions, and other weather warnings. Newer radios can be set to play county-specific alerts. NOAA Weather Radio broadcasts can usually be heard as far as 40 miles from a transmitter, although a good quality antenna may be needed for reliable reception in some urban areas. 

NOAA - Weather Radios can be purchased at many electronic stores.

Wireless Emergency Alerts

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Imagine this: You’re driving down the highway, humming along to your favorite tunes, when the cell phone stowed in your bag suddenly makes a strange noise. To investigate, you take the next exit and safely pull over to check the screen. Good thing you did: Your phone just alerted you to a tornado a few miles away in same county you’re driving through.

Sound plausible? It is. America’s wireless industry is helping to build a Weather-Ready Nation through a nationwide text emergency alert system, called Wireless Emergency Alerts (WEA), which will warn you when weather threatens. Read the rest of the article on