Editing Emergency Alert System (section)

===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 (following parameters set by the broadcaster).

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 {{Audio|1050Hz Tone.ogg|1,050&nbsp;Hz}} on a [[NOAA Weather Radio]] station. On commercial broadcast stations, a {{Audio|Emergency Alert System Attention Signal 20s.ogg|"two-tone"}} attention signal of 853&nbsp;[[Hertz (frequency)|Hz]] and 960&nbsp;Hz [[sine wave]]s 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. The "two-tone" system is no longer required as of 1998, and is to be used only for audio alerts before EAS messages.<ref name="cfr47">{{cite web |date=July 26, 2014 |title=United States Code of Federal Regulations – 47 CFR 11.61 – Tests of EAS procedures |url=http://www.gpo.gov/fdsys/pkg/CFR-2013-title47-vol1/pdf/CFR-2013-title47-vol1-sec11-61.pdf |url-status=live |archive-url=https://web.archive.org/web/20140726180608/http://www.gpo.gov/fdsys/pkg/CFR-2013-title47-vol1/pdf/CFR-2013-title47-vol1-sec11-61.pdf |archive-date=July 26, 2014 |access-date=July 19, 2014 |publisher=access.gpo.gov}}</ref> 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 [[Audio frequency-shift keying|AFSK]] "EOM", or [[End of Message]], which is the text <code>NNNN</code>, preceded each time by the [[Binary numeral system|binary]] 10101011 calibration.