When a Alerting weather warning is issued for the area which a station covers, certain weather radios are designed to turn on or sound an alarm upon detection of a 1050 Hz tone, issued for ten seconds immediately before the warning message. The specification calls for the NWS transmitter to send the 1050 Hz tone for 10 seconds, and the receiver to react to it within 5 seconds (any extra tone time over and above the reaction time is considered as part of the alerting mechanism). This system simply turns on the audio of every muted receiver within the radio horizon of the transmitter (i.e. any receiver within the transmitter's "footprint"). Additional external devices such as a strobe light which attaches via an accessory port are also available to provide a more immediate and visible warning.
Newer radios can instead detect a digital-over-audio protocol called Specific Area Message Encoding or SAME, which allows the users to program their radios for specific geographical areas of interest and concern, rather than for an entire regional broadcast area. The newer radios also have lit LEDs which indicate whether the message sent out is a warning, advisory or watch in the color order of red for a warning, amber for a watch, and either yellow or green for a statement or advisory, mainly both to give quick reference for those who may not have time to hear the whole alert, and to give those who are hearing impaired some way to be alerted to the oncoming event. The SAME code is broadcast, followed by the 1050 Hz tone. This has the advantage of eliminating the numerous "false alarms" for the 1050 Hz weather alerts that may apply to an area 100 or 150 miles (240 km) distant. The SAME codes are mostly aligned along county lines using the standard US Government FIPS county codes. Most modern SAME equipped radios can be programmed to receive alerts for more than one FIPS code if the user is located along a county boundary.
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