The necessity for a signal sound to inform or warn members of a society is not a recent invention. Even in the Stone Age, drums and animal horns were used to spread messages far and wide. After the discovery of various metals, people began to manufacture signal horns for military use. Instruments like trumpets and trombones are derived from these early horns. As we can see, alarm systems and siren sounds have been part of our society since the dawn of mankind.
The use of alarm bells goes back all the way to the Egyptians and the time of the Pharaos. These so-called plate bells were hung from shelves so that their distinctive sound could be heard from far away. This technique is still being used today, except that plate bells and forged bells have been replaced with cast bells. For many centuries, storm bells and alarm bells were used to warn village and city dwellers from fires and attacking barbarians.
After the Industrialisation, the ambient noise of a mechanised society necessitated a new kind of alarm system. The first sirens were steam-powered pipes used on steamships, because traditional bells were no longer loud enough to overpower the noise of the engines.
Air Raid Alarm Sounds
Thanks to electricity and the invention of the motorised siren, this type of siren was widely adopted before and during the Second World War. The undulating, howling sound of the siren was highly characteristic, which made it an efficient warning signal ahead of air raids. It also became synonymous with the terror of falling bombs -- death dealt from the skies. An entire generation was scarred forever by the sound of the motorised siren.
During the Cold War, sirens were no longer used to warn of air raids. Instead, they became alarm systems for possible nuclear attacks. In Germany, the term 'alert' replaced the previous 'air raid warning'. A shortened, one-minute siren alarm was devised to alert citizens of a possible attack.
In post-WWII England, alarm sirens were assigned a new meaning: alerting people to the threat of a nuclear attack. They were also used to warn people of floods and freak weather, as well as escaped prisoners or highly dangerous mental-health patients.
Electric Alarm Sirens
Electric alarm sirens are not only used in household alarm systems or fire alarms, they are also quite common in civil defence structures (although in larger versions). Electric alarm sirens create the siren signal with the help of a loudspeaker and an amplifier. A horn directs the siren sound into whatever direction is desired. Electric sirens come with the benefit of having few mechanical parts that need maintenance (except for the loudspeaker). These sirens are therefore much lighter than their mechanical counterparts. Thanks to the electric transmission of the siren signal, undulating sounds can be created. It is also possible to use the siren as a public-address system.
Flood Alarm Sounds
In Switzerland, the flood alarm consists of twelve constant low-frequency sounds that last 20 seconds each (with 10 seconds intervals between them). If you hear the flood alarm, you should get out of the affected area immediately. Flood alarm sirens are only installed in high-risk areas such as dams. If a dam breaks and a flood wave is released, a general (undulating) siren alarm will go off in the areas at risk.
The term 'tsunami' became a household word after 2004 when a massive sea-quake in the Indian ocean triggered a series of devastating flood waves. Indonesia was hit particularly hard, along with other countries on the Indian ocean: Thailand, India and Sri Lanka all suffered massive devastation from the tsunamis. To prevent future disasters of a similar kind and warn coastal populations about sea-quakes and tsunamis, many countries installed early warning systems. Sirens and info displays were set up along beaches to alert people of approaching tsunamis by sounding an alarm or displaying a text message. Tsunamis are the result of sea-quakes or underwater rock-falls. Depending on the location of the quake, the shock wave of the tsunami might take quite a bit of time until it hits the shore. Early warning systems use satellites and buoys to identify shockwaves and trigger alarms.
In Thailand, tsunami sirens alert the population and the tourists of the approaching danger in more densely populated areas. Sirens are also used to warn of tsunamis in other countries. The type of siren and alarm used depends on the region and the country. The goal is always the same, though: to warn of the approaching danger.
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