Who knows what this is?

[math311]

This klaxon thing will produce the distinctive wail of an air raid siren and appears to be quite old. We are using it on a float for a parade, and we would like to know what it might really be called. The little metal plate says it is an "automatic burglar alarm". A kid also brought in some 2 Mb hard drives from long ago. I guess i cant upload a pic, but it has an electric motor on back, an air intake section with spinning fan/blades, and a bell that opens big. 12 volts

[Al Skierkiewicz]

Math,
Can you give us an idea of what size this device is? Old car alarms often used a siren type noise maker. They had a small electric motor at one end (about half as big as a CIM) usually painted red or black. The noise maker end looks like a chromed soup can with odd shaped slots cut into the circumference. The motor then spins up another cylinder inside the can also with odd shaped slots. The rushing air coupled with the slots produces a shrill noise much like an old fire engine or police car. Typical size was about 10" long and 2-3" in diameter. Some had a relay mounted on the outside and some just had a wire coming out one end. The other wire is tied internal to the metal case.

[TroyCDH]

As a fan of old black and movies from the 30s & 40s I recently saw a movie (forgot the name) where the burglars are practicing for days to disarm an automatic burglar alarm. Then they pull the big bank job!

It was simply some magnetic switches on the doors and windows that activated the alarm. Compared to having a human security officer 24-7 it would be considered automatic for the 30s.

[DonRotolo]

Originally Posted by math311

we would like to know what it might really be called.

It's called a "siren".

12 volts does not necessarily indicate automotive use, as many building alarms work off 12 volts as well.