The Contra Costa County Community Warning System (CWS) is recognized as one of the nation’s most modern and effective all-hazard public warning systems. The CWS is a partnership of the Office of the Sheriff, the Health Services Department, other government agencies, industry, news media and the non-profit Community Awareness & Emergency Response (CAER) organization, all striving to deliver time-sensitive and potentially life-saving information to the people of Contra Costa County.



picture of an aerial siren


The CWS may use sirens to alert you to a possible hazard in your area. It could be for any number of hazards and is sounded to draw your attention away from your daily activities. No matter the hazard, the best first protective action is to Shelter, Shut and Listen.

Sirens are tested on the first Wednesday of every month at 11:00am. For a siren location map click here.

Below is an example of a CWS siren sound:

Voice, Text and Email Alert Messages

The CWS Telephone Emergency Notification System (TENS) is used for call-out in case of emergency.

A computerized system makes telephone calls to the known telephone numbers in the vicinity of the hazard based on the incident-specific issues. To streamline for fast activation in an emergency, the areas around certain known places were predefined, so activation is faster.

Telephone Emergency Notification System (TENS) Zones

These predefined areas are the “TENS Zones”. Follow the links below to access the maps for the predefined areas:

NOAA Weather Radio

CWS uses the National Weather Service to provide emergency alerts and information for major non-weather related emergencies. Weather radios are an inexpensive and reliable way to receive these alerts. These devices can be battery powered to provide a means of receiving emergency alerts if your power is out. Learn more about NOAA Weather Radios here.

NOAA radio

Emergency Alert System (EAS) and Wireless Emergency Alerts (WEA)

The CWS is designed to provide specific information directly to the media through the Emergency Alert System. The EAS interrupts TV and radio broadcasts to deliver major local, regional, and national emergency alerts. Following the initial alert, TV and Radio stations provide ongoing status reports and information.

The CWS uses a federal system that sends text alerts to your smartphone during major emergencies, no registration needed! Check with your cell phone service provider to see if your cell phone can receive Wireless Emergency Alerts.

To learn more about EAS and WEA click here. To register your address for future alerts, click here.