All clear

During the First World War, the Metropolitan Police introduced their first air raid warning system in London in 1917, which consisted of police officers detonating maroons (a type of loud firework) and the "all clear" was sounded by Boy Scout buglers.Ian Frederick William Beckett (2006), Home Front 1914-1918: How Britain Survived the Great War, The National Archives, {{ISBN|978-1-903365-81-6}} p. 187

Immediately before the Second World War, a network of sirens had been established in towns across the United Kingdom; the "alert" was given by a rising and falling tone and the "all clear" by a continuous tone.{{cite web |url=https://www.bbc.co.uk/learning/schoolradio/subjects/history/ww2clips/sounds/all_clear_siren |title=School Radio - Warning sounds: 'All clear' siren |last1= |first1= |last2= |first2= |date= |website=www.bbc.co.uk |publisher=BBC |access-date=31 August 2015 |quote=}} The sirens remained in place during the Cold War but instead of being the responsibility of local police forces, the alarms were activated by the United Kingdom Warning and Monitoring Organisation. Following an air raid, the "all clear" would only be sounded if no nuclear weapons had been used, or when any nuclear fallout was deemed by the Royal Observer Corps to have reached safe levels, which might have been up to two weeks later. The system was discontinued in 1992.{{cite web |url=http://www.ringbell.co.uk/ukwmo/Page211.htm |title=British Nuclear Warning System |last=Scanlon |first=Steve |date= |website=www.ringbell.co.uk/ukwmo/ |publisher= |access-date=11 December 2020}}

The following is a list of countries that use All Clear on sirens:

1. Denmark
2. Sweden
3. Singapore
4. Kuwait
5. U.S. (some areas)
6. Afghanistan (for instance, Kandahar)
7. Canada
8. Israel

1. Netherlands
2. South Korea
3. China
4. U.S. (some areas)

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Category:Civil defense

Category:Emergency population warning systems