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Commercial Mobile Telephone Alerts (CMAS)

The FCC took a number of steps in facilitating the ability of consumers to receive emergency alerts through their wireless phones. In 2008, the Commission issued a series of orders adopting requirements for a Commercial Mobile Alert System (CMAS), a system by which commercial mobile service (CMS) providers may transmit emergency alerts to their subscribers, if they choose to do so.


Under the rules adopted by the FCC:



  • The CMAS would consist of an end-to-end system by which an Alert Aggregator/Gateway would receive, authenticate, validate and format Federal, state, tribal and local alerts and then forward them to the appropriate CMS Provider Gateway. The CMS Provider Gateway and associated infrastructure would process the alerts and transmit them to subscriber handsets.

  • Subscribers could receive up to three classes of text-based alerts, such as Presidential, Imminent Threat (e.g., tornado), and Amber Alerts.

  • Subscribers would automatically receive these alerts if they have a CMAS-compatible handset. There would be no subscriber opt-in requirements.

  • To ensure that people with disabilities have access to alerts, CMS providers must provide a unique audio attention signal and vibration cadence on CMAS-compatible handsets.

  • CMS providers generally must transmit alerts to areas no larger than the targeted county. However, CMS providers may transmit to areas smaller than the county if they choose to do so.

  • Subscribers receiving services pursuant to a roaming agreement will receive alert messages if: (1) the operator of the roamed upon network is a participating CMS provider; and (2) the subscriber's mobile device is configured for and technically capable of receiving alert messages from the roamed-upon network.

  • CMAS messages will not preempt calls in progress.

The FCC's actions implements provisions of the Warning, Alert and Response Network Act ("WARN Act") which, among other things, allows CMS providers to voluntarily transmit emergency alerts to their subscribers. The FCC's actions also implement one of its highest priorities - to ensure that all Americans have the capability to receive timely and accurate alerts, warnings and critical information regarding disasters and other emergencies irrespective of what communications technologies they use. These actions also recognize the important role that wireless services play in consumers' lives. Wireless service has progressed beyond voice communications and now provides subscribers with access to a wide range of information critical to their personal and business affairs. In times of emergency, Americans increasingly rely on wireless telecommunications services and devices to receive and retrieve critical, time-sensitive information. A comprehensive wireless mobile alerting system would have the ability to alert people on the go in a short timeframe, even where they do not have access to broadcast radio and television or other sources of emergency information. Providing critical alert information via wireless devices will ultimately help the public avoid danger or respond more quickly in the face of crisis, and thereby save lives and property.


On September 8, 2008, CMS providers began filing their letters of intention to participate or not to participate in CMAS. The CMAS Registry lists all CMS providers that have filed election letters with the Commission, including non-participation, participation "in part," participation "in whole," and withdrawals of a previous election to participate, either "in part" or "in whole."


FCC Master WEA Carrier Registry File (xls)


Last updated: 12/17/2013. Please note that the Excel file contains four tabs providing information on carriers that have elected not to participate, carriers participating "in part", carriers participating "in whole", and carriers that have withdrawn a previous election to participate either "in whole" or "in part".


For further information concerning the FCC CMAS Registry, or to notify the Commission of changes to the CMAS Registry, contact Timothy May at timothy.may@fcc.gov.


CMAS Documents


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