The siren was made by Universal Security Instruments. It was sold as part of a kit that included a key-operated on/off switch and four door jamb switches. As others have already stated, the kit was sold by many retailers including Pep Boys and Western Auto, but it was J.C. Whitney that sold the most. This one is from the late 60's to early 70's. Later versions had the bell horn integrally die cast with the stator. The whole kit was less than $40.00 and the siren could be purchased separately (minus the relay) for $23.00.
It's amazing how many of these things show up on eBay listed as "Old Fire Truck Siren"'!