Emergency Signal Siren Sign along country roadside.
A civil defense siren (also known as an air-raid siren or tornado siren) is a siren used to provide emergency population warning of approaching danger and sometimes to indicate when the danger has passed. Som United States[edit] In the United States, several sets of warning tones have been used which varied over time, by government structure, and by manufacturer. The initial alerts used during World War II were the Alert Signal (a 3–5 minute steady continuous siren tone), and the Attack Signal (a 3–5 minute wail siren tone, or series of short tone bursts on devices incapable of wavering, such as whistles). The Victory Siren manual stated that when manual generation of the warbling tone was required, it could be achieved by holding the Signal switch on for 8 seconds and off for 4 seconds. In 1950, the Federal Civil Defense Administration revised the signals, naming the alert signal "red alert" and adding an "all-clear" signal, defined as three one-minute steady blasts, with two minutes of silence between blasts.[3] Beginning in 1952, the Bell and Lights Air Raid Warning System,[4] developed by AT&T, was made available to provide automated transmission of an expanded set of alert signals: Red Alert (attack imminent) Yellow Alert (attack likely) White Alert (all-clear) Blue Alert (undefined) The Yellow Alert and Red Alert signals correspond to the earlier Alert Signal and Attack Signal, respectively, and the early Federal Signal AR timer siren control units featured the Take Cover button labeled with a red background, and the Alert button labeled with a yellow background. Later AF timers changed the color-coding, coloring the Alert button blue, the Take Cover button yellow, and the Fire button red (used to call out volunteer fire fighters), thus confusing the color-coding of the alerts. In 1955, the Federal Civil Defense Administration again revised the warning signals, altering them to adapt to deal with concern over nuclear fallout. The new set of signals were the
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Location: Salem, New Jersey
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