I remember, as a kid (long time ago), they blew those sirens off when they had air-raid drills - and everybody had get off the street. We'd go in stores, or wherever was closest. People with an underground air raid shelter had the best hideouts. Some buildings still say where the shelter is - usually in the basement. There were air-raid civil defense volunteers also, checking the areas out.
They also made us hide under the desks at school - in case the Russians dropped an atomic bomb on us.
Check out this monster siren from Chrysler - it's the type that was used in large cities: It's 3 tons, 30,000 Watts, with a 4 Mile Range
VictorySiren.com - Internet Home for the Chrysler Air Raid Siren