Like HowStuffWorks on Facebook!

How Emergency Notifications Work

        Tech | E-mail & Messaging

Non-Discriminating Alarms

An air raid siren is the best example of a non-discriminating emergency notification. The siren's warning tone or audio message is delivered to everyone within audible range of the broadcast, no matter who they are or what equipment they own. All other types of warnings rely on communications devices such as televisions, radios, phone, computers or handhelds, to deliver a message.

Unlike targeted warnings, an air-raid siren is designed to reach a broad swath of the population, not just those most likely to be affected by the emergency.

"Air-raid siren" is really a misnomer. Very few long-range warning systems are still used for the express purpose of alerting citizens to a military attack. Some common applications of modern warning sirens include:

  • Volunteer fire calls
  • Severe storm warnings
  • Tornado warnings
  • Hurricane warnings
  • Tsunami warnings
  • Dam failure alerts
  • Chemical spill alerts

Many modern warning sirens begin with a tone or series of tones, then play a recorded message, often encouraging citizens to turn on their televisions or radios for further instructions. Those TV and radio broadcasts are part of another non-discriminating warning called the Emergency Alert System (EAS).

The EAS, formerly known as the Emergency Broadcast System, was created by the Federal Communications Commission (FCC) as a way for the president to speak to the country in a time of crisis. In 1963, state and local emergency officials were also permitted to use to the warning system, which now broadcasts over all TV and radio networks, including air, cable, satellite and digital channels.

Messages from the EAS are slightly more targeted than warning sirens, because state and local officials can choose over which stations to broadcast their message based on the areas most affected by the emergency. The EAS also teams with the National Weather Service to provide real-time storm and severe weather information to participating stations. The messages can even be broadcast in Spanish to Spanish-language stations in the U.S.

The FCC is looking into expanding the system to "take full advantage of digital and other emerging communications technologies." Private companies are competing to corner the emergency notification market. Click on the next page to read more about these highly targeted emergency notifications.