A fact of life is that severe weather and civil disasters occur. While precautions are taken to avoid disasters, combinations of circumstances sometimes overcome such precautions We are yet virtually powerless to control the weather. Because we are often incapable of preventing disasters and have no means for nullifying or moving weather disturbances, our survival instincts lead us to devise methods for minimizing the toll of human lives and injuries that can result from severe weather and disasters. Thus, the weather is carefully monitored and forecast and warnings are issued when threatening weather patterns occur to allow persons in affected areas to take precautions. Similarly, fire and police departments and the military services are charged with the responsibilities, often overlapping, of dealing with and minimizing the loss of life and injuries resulting from fires, explosions, chemical leaks and spills, civil disturbances, air raids, and the like.
Several warning methods currently exist for alerting populations to tornadoes and other severe weather and emergencies. Television stations often superimpose an indicia indicating a thunderstorm watch and, if very severe weather is impending, interrupt normal programming to notify viewers of a tornado or severe storm warning. Deficiencies of this warning method are that a television set must be turned on, actively watched, and tuned to a local station to receive the warning. Many communities have a system of remotely controlled, diesel powered sirens, commonly referred to as civil defense or air raid sirens, to warn residents of emergencies. Such sirens are susceptible to mechanical breakdowns and must be taken out of service periodically for maintenance. At times local police and fire departments patrol the streets of neighborhoods with their sirens activated and periodically announcing emergencies over loudspeakers. This warning method may be ineffective because of inability to hear the sirens or announcements because of storm noise, distance from the siren, interfering noise levels within a residence, location of persons within a residence, or persons asleep in a residence. Siren type warning systems do not indicate the specific location of the impending emergency and often do not provide an "all clear". Because response to emergencies is usually disruptive of normal activities, false warnings or warnings which do not apply to particular individuals cause such persons to tend to ignore sirens and other relatively general types of warnings.
In a warning system currently in use by the National Weather Service, continuing weather bulletins are broadcast on a VHF frequency. Whenever severe weather threatens, an alert is broadcast which triggers an audible alarm in special receivers, such as the Weatheradio units available from Tandy Corporation. However, since the coverage areas of the broadcast stations usually encompass a number of county sized areas, it is possible to receive an alert on a receiver in an area to which the alert has no actual significance. At best, this amounts to a nuisance. Additionally, when an alert is triggered in such a receiver, it must be muted manually by the user since the system does not incorporate a broadcast "all clear" signal.
What is needed is a system of alerting populations to emergency conditions which is geographically specific, which is also specific as to the type of emergency condition, and which cannot be easily ignored or defeated by the persons for whom the warning is directed.