(WHTM) — The Emergency Alert System is used in many different events, such as weather warnings, public safety warnings, and the generic, yet somewhat annoying, required weekly test.
But, did you know that all of those scary, annoying noises you hear when an emergency alert comes through actually have a meaning?
By definition, the Federal Communications Commission (FCC) defines the Emergency Alert System (EAS) as a national public warning system commonly used by state and local authorities to deliver important emergency information, such as weather and AMBER alerts, to affected communities over television and radio.
These alerts are different than the Wireless Emergency Alerts, which come through on cell phones.
The EAS was established on Jan. 1. 1997 and replaced the older Emergency Broadcast System (EBS).
There are four general parts to every EAS broadcast that is sent out to weather radios and broadcast stations.
- SAME header
- Attention Tone
- End of Message Tones
The Specific Area Message Encoding (SAME) header is a digital code before and after each alert message through whatever agency is sending the alert. It is the three digital bursts before the attention tone. This signal encodes locations for the alert and is useful for specialized encoding and decoding equipment at broadcasting stations to automatically filter alert messages, to make sure the alert is for their location.
It was developed by the National Weather Service (NWS) for use on its NOAA Weather radio and was later used by the Federal Communications Commission for the EAS.
The receivers that get the SAME header decode this message which contains information on a type of message, the area affected, and the expiration time of the message. The National Weather Service has a maximum message expiration time of six hours. This SAME header also contains an event code, and a full list of those can be seen here.
After the SAME header bursts, an attention tone is used. The NWS runs the attention tone for 10 seconds, however, the tone can be run between eight to 25 seconds.
Depending on the receiver of the attention tone, this tone may sound different. On NOAA weather radios, the tone is broadcast as a 1050 hertz tone. On a broadcasting station, a two-tone attention signal of 853 Hz and 960 Hz are used.
This part of the EAS is what the alert is about, giving details about the watch, warning or advisory, and relaying instructions if necessary.
End Of Message Tones
Every EAS message ends with End of Message Tones (EOM), to let the receiver know that the EAS message has concluded.
According to the NWS, about 90% of all EAS activations are usually for short-duration weather warnings and watches. Alerts such as AMBER alerts or evacuation warnings can also be broadcasted through NOAA weather radios if a local, state, or federal emergency management agency requests it.
For more information about the Emergency Alert System, click here.
The FCC’s Emergency Alert System rules are intended to ensure that national activation would enable the president to communicate with the public within 10 minutes from anywhere. However, this has never been used since its inception and only national tests of the system.