What is Thunderbolt siren?

A Civil Defense siren made in 1952.

Models
Thunderbolt 1000: single toned chopper that can do Alert and Attack signal
Thunderbolt 1000T: a dual toned version of the Thunderbolt 1000
Thunderbolt 1003: a dual toned chopper with solenoids that gives it the ability to do the Hi-Lo signal