What is the Commercial Mobile Alert System (CMAS)?

The Commercial Mobile Alert System (CMAS) is a system that enables authorized government agencies to send a geographically-targeted message to the public regarding an emergency situation. CMAS, also known as the Wireless Emergency Alerts (WEA) system, is a free service that delivers alerts to mobile devices such as cell phones and wireless routers.


CMAS has been in operation since April 2012 following the WARN Act (Warning, Alert and Response Network Act) of 2006, which mandated the creation of a nationwide alert system. CMAS allows government agencies to broadcast messages in three categories:

  • Presidential Alert: Emergency alerts issued by the President of the United States or their designee. These alerts are issued for national emergencies or other significant events that pose a grave threat to the safety of the American public.
  • Imminent Threat Alert: Alerts related to an imminent, life-threatening situation such as a terrorist attack, imminent threats to public safety, severe weather events, or other disasters.
  • AMBER Alert: Alerts related to the disappearance of a child. These alerts include information such as a description of the child and the vehicle they may be traveling in.

How does CMAS work?

CMAS works by utilizing a unique technology called Cell Broadcast (CB), which enables messages to be sent to all mobile devices in a specific geographical area. The CB technology was first developed in the 1980s and was designed to deliver messages to all mobile devices within range of a given cell tower.

With CMAS, government agencies can send messages to mobile devices within a specific location, such as a city, county, or state. When an emergency message is sent, mobile devices within the targeted area receive an audible alert, a vibration, and a message on their phone’s home screen. The messages are sent based on the device’s current location, not where the device is registered to. This ensures that people traveling or living temporarily in a particular area receive the alerts based on where they are currently located.

Consumer cellular phone

What to do when receiving a CMAS alert on your mobile device?

When you receive a CMAS alert on your mobile device, it is important to read the message carefully and follow any instructions given. The alert will include information such as the type of emergency, location, and recommended actions to take. Here are some tips on what you should do:

  1. Take the alert seriously: CMAS messages are only sent during emergencies, and it is important to take them seriously and follow any instructions given.
  2. Stay informed: After receiving the alert, it is important to stay informed about the situation through local news and emergency management agencies. You can also follow social media channels for updates.
  3. Take appropriate actions: Depending on the nature of the emergency, the message will give instructions on what to do. For example, if a tornado warning is issued, the message may instruct you to take shelter immediately.
  4. Help others: If you are in a position to help others, such as co-workers or neighbors, provide assistance as needed.

FAQs about CMAS

1. Will I receive CMAS alerts if I’m traveling outside of my home area?

Yes, you will receive CMAS alerts based on your mobile device’s location at the time the message is sent. This means that if you are traveling outside of your home area and are within the targeted geographic area of an emergency message, you will receive the alert on your device. This is because CMAS uses the current location of your device, not where your device is registered to.

2. Can I opt-out of CMAS alerts?

No, CMAS alerts are mandatory and cannot be opted out of. This is to ensure that the maximum number of people receive emergency alerts during a crisis. However, you can choose to turn off the sound or vibration notifications for messages from CMAS.

Video Explanation of CMAS:

In summary, CMAS is a free notification system that allows authorized government agencies to send emergency alerts to mobile devices within a specific geographic area. It uses Cell Broadcast technology to deliver messages and is divided into three categories of alerts – Presidential, Imminent Threat, and AMBER. When you receive a CMAS alert, it is crucial to take it seriously and follow any instructions given to stay safe. While you cannot opt-out of CMAS messages, you can turn off the sound or vibration notifications. Stay informed about CMAS and keep yourself and your loved ones safe during emergencies.