Chrysler air raid siren
From Dodge Wiki
The Chrysler Air Raid Siren was the most powerful and loudest Air raid siren ever made.
Known as "Big Red" and built during the post-World War II Cold War from 1952-1957 by Chrysler, its power plant contained a newly-designed FirePower Hemi V-8, 331 cubic inch 180 horsepower (130 kW) Engine.
Its six horns, produced by Victory Sirens, were three feet long and produced a sound that some say caused a fire in a Detroit testing facility. The siren can be heard from a distance of four to five miles (8 km) away and had an output of 138 Decibel and 30,000 Watts. It is 12 feet (3.7 m) long, built atop a quarter section of a Dodge truck chassis rail, and weighs an estimated three Tons.
In 1952, the cost of a Chrysler Air Raid siren was $5,500.00.  The United States government helped buy sirens for selected state and county law enforcement agencies around the country. In Los Angeles County, six were placed around key locations of populated areas, and another ten were sold to other government agencies in the California. Most of these "Big Red Whistles" (as they were nicknamed by civilians) were only used for test purposes. Some were located so remotely that they deteroriated, due to lack of maintenance.
Some sirens are still located above buildings and watchtowers. However, many of these are rusted, and in some cases the salvage price is less then the cost to remove them. Some have been restored and placed in museums or on trailers to exhibit to the public.