The Thunderbolt siren is a discontinued electro-mechanical warning siren

Civil defense siren

A civil defense siren is a mechanical or electronic device for generating sound to...

 that was once manufactured in the United States by Federal Signal Corporation

Federal Signal Corporation

Federal Signal Corporation is a global corporation with about 2,800 employees and annual revenue of about US$727 million. Oak Brook, Illinois-based Federal Signal designs, develops and deploys solutions intended to protect people, property and the environment under brands such as Federal Signal,...

. The Thunderbolt siren consists of three major components: the blower, rotator and siren chopper. The blower, which is made up of a motor-driven Roots-type supercharger, supplies the large volume of air for the siren head. It is housed inside a large rectangular box typically found at the base of the siren head.