Emergency Alert System
The Emergency Alert System is a national warning system in the United States designed to allow authorized officials to broadcast emergency alerts and warning messages to the public via cable, satellite and broadcast television and AM, FM and satellite radio. Informally, Emergency Alert System is sometimes conflated with its mobile phone counterpart Wireless Emergency Alerts, a different but related system. However, both the EAS and WEA, among other systems, are coordinated under the Integrated Public Alert and Warning System.
The EAS, and more broadly IPAWS, allows federal, state, and local authorities to efficiently broadcast emergency alert and warning messages across multiple channels. The EAS became operational on January 1, 1997, after being approved by the Federal Communications Commission in November 1994, replacing the Emergency Broadcast System, and largely supplanted the similar Emergency Override System, though the latter is still used from time to time. Its main improvement over the EBS, and perhaps its most distinctive feature, is its application of a digitally encoded audio signal known as [|Specific Area Message Encoding], which is responsible for the “screeching” or “beeping” sounds at the start and end of each message. The first signal is the "header" which encodes, among other information, the alert type and locations, or the specific area that should receive the message. The last short burst marks the end-of-message. These signals are read by specialized encoder-decoder equipment. This design allows for automated station-to-station relay of alerts to only the area the alert was intended for.
Like the Emergency Broadcast System, the system is primarily designed to allow the president of the United States to address the country via all radio and television stations in the event of a national emergency. Despite this, neither the system nor its predecessors have been used in this manner. The ubiquity of news coverage in these situations, such as during the September 11 attacks, has been credited to making usage of the system unnecessary or redundant. In practice, it is used at a regional scale to distribute information regarding imminent threats to public safety, such as severe weather situations, Amber alerts, and other civil emergencies.
It is jointly coordinated by the Federal Emergency Management Agency, the FCC, and the National Oceanic and Atmospheric Administration. The EAS regulations and standards are governed by the Public Safety and Homeland Security Bureau of the FCC. All broadcast television, broadcast and satellite radio stations, as well as multichannel video programming distributors, are required to participate in the system.
Technical concept
Messages in the EAS are composed of four parts: a digitally encoded Specific Area Message Encoding header, an attention signal, an audio announcement, and a digitally encoded end-of-message marker.The is the most critical part of the EAS design. It contains information about who originated the alert, a short, general description of the event, the areas affected, the expected duration of the event, the date and time it was issued, and an identification of the originating station.
There are 79 radio stations designated as National Primary Stations in the Primary Entry Point System to distribute presidential messages to other broadcast stations and cable systems.
The National Emergency Message is the notice to broadcasters that the president of the United States or their designee will deliver a message over the EAS via the PEP system. The government has stated that the system would allow a president to speak during a national emergency within 10 minutes.
| Operational area | Station | Citations |
| National | NPR, PRN, SXM | |
| United States Virgin Islands | WSTA | |
| Puerto Rico | WKAQ | |
| Maine | WGAN | |
| New Hampshire, Vermont, Massachusetts, Rhode Island | WBZ | |
| Connecticut | WTIC | |
| New York City, New Jersey | WABC | |
| Northeast New York | WROW | |
| South Central New York | WBNW-FM | |
| North Central New York | WHEN | |
| Western New York | WHAM | |
| Delaware, Eastern Pennsylvania | WTEL, WHYY-FM | |
| Western Pennsylvania | KDKA | |
| West Virginia | WCHS | |
| Maryland | WBAL | |
| District of Columbia | WFED | |
| Eastern Virginia | WTAR | |
| Central Virginia | WRXL | |
| Western Virginia | WPLY | |
| Eastern North Carolina | WSFL-FM | |
| Central North Carolina | WQDR-FM | |
| Western North Carolina | WBT | |
| Upstate South Carolina | WKVG | |
| Downstate South Carolina | WCOS-FM | |
| Georgia | WMAC, WSRV | |
| North Florida | WOKV | |
| Central Florida | WFLF | |
| South Florida | WAQI | |
| Alabama | WJOX | |
| Mississippi | WMSI-FM | |
| East Tennessee | WJCW, WJXB-FM | |
| Middle Tennessee, Southwest Indiana | WSM | |
| West Tennessee | WREC | |
| Kentucky, Southwest Ohio, Southeast Indiana | WLW | |
| Northeast Ohio | WTAM | |
| Michigan | WJR | |
| Northwest Indiana, Northern Illinois | WLS | |
| Southern Illinois, Eastern Missouri | KMOX | |
| Wisconsin | WTMJ | |
| Minnesota | WCCO | |
| Iowa | WHO | |
| Central Missouri | KTXY | |
| Western Missouri | WHB | |
| Arkansas | KAAY | |
| Southeast Louisiana | WWL | |
| Northwest Louisiana | KWKH | |
| Central Texas | KLBJ | |
| North Texas | WBAP, KSCS | |
| Southeast Texas | KTRH | |
| West Texas | KROD | |
| Oklahoma | KRMG, KOKC | |
| Nebraska | KRVN | |
| North Dakota, South Dakota | KFYR | |
| Montana | KERR | |
| Wyoming | KTWO | |
| Colorado, South Dakota | KOA | |
| New Mexico | KKOB | |
| Arizona | KFLT | |
| Utah | KSL | |
| Idaho | KBOI | |
| Northern Nevada | KKOH | |
| Southern Nevada | KXNT | |
| San Diego area | KOGO | |
| Southern California | KFI, KNX | |
| Central California | KMJ | |
| Northern California | KCBS | |
| Hawaii | HEMA | |
| American Samoa | WVUV-FM | |
| Guam and Northern Marianas | KTWG | |
| Oregon | KOPB-FM, KPNW | |
| Washington | KIRO | |
| Alaska | KFQD |
Primary Entry Point stations
The National Public Warning System, also known as the Primary Entry Point stations, is a network of 77 radio stations that are, in coordination with FEMA, used to originate emergency alert and warning information to the public before, during, and after incidents and disasters. PEP stations are equipped with additional and backup communications equipment and power generators designed to enable them to continue broadcasting information to the public during and after an event.Beginning with WJR Detroit and WLW Cincinnati in 2016, FEMA began the process of constructing transportable studio shelters at the transmitters of 33 PEP stations, which feature broadcasting equipment, emergency provisions, a rest area, and an air filtration system. NPWS project manager Manny Centeno explained that these shelters were designed to " the survivability of these stations to include an all hazards platform, which means chemical, biological, radiological air protection and protection from electromagnetic pulse."
Communication links
The FEMA National Radio System "Provides Primary Entry Point service to the Emergency Alert System", and acts as an emergency presidential link into the EAS. The FNARS net control station is located at the Mount Weather Emergency Operations Center.Once an EAN is received by an EAS participant from a PEP station the message then "daisy chains" through the network of participants. "Daisy chains" form when one station receives a message from multiple other stations and the station then forwards that message to multiple other stations. This process creates many redundant paths through which the message may flow, increasing the likelihood that the message will be received by all participants and adding to the survivability of the system. Each EAS participant is required to monitor at least two other participants.
EAS header
Because the header lacks error detection codes, it is repeated three times for redundancy. EAS decoders compare the received headers against one another, looking for an exact match between any two, eliminating most errors that can cause an activation to fail. The decoder then decides whether to ignore the message or to relay it on the air if the message applies to the local area served by the station.The SAME header bursts are followed by an EAS attention tone, which lasts between 8 and 25 seconds, depending on the originating station. The tone is on a NOAA Weather Radio station. On commercial broadcast stations, a attention signal of 853 Hz and 960 Hz sine waves is used instead, the same signal used by the older Emergency Broadcast System. These tones have become infamous, and can be considered both frightening and annoying by listeners; in fact, the two tones, which form approximately the interval of a just major second at an unusually high pitch, were chosen specifically for their ability to draw attention, due to their unpleasantness on the human ear. The SAME header is equally known for its shrillness, which many have found to be startling. These tones are illegal to play on television or radio when there is not an actual emergency; doing so would result in disciplinary action or be fined for misuse or unauthorized playback of the tones. The "two-tone" system is no longer required as of 1998, and is to be used only for audio alerts before EAS messages. Like the EBS, the attention signal is followed by a voice message describing the details of the alert.
The message ends with 3 bursts of the AFSK "EOM", or End of Message, which is the text
NNNN, preceded each time by the binary 10101011 calibration.