While searching around for vintage siren material, I ran across this article detailing one of those "interesting" attempts at creating an air raid siren.
http://www.leicestermercury.co.uk/Detec ... story.html
This rotating directional siren was built by Parmeko Ltd. and mounted on the old Lewis's Tower in Leicester (England). It used two perforated discs which blew air into the directional horns, producing sound. This was actually built just before World War 2. Unfortunately it was a short lived creation as the city decided to buy smaller and more conventional sirens from Gent's - only one other "Parmeko" siren was built and it went to a naval dockyard. Neither sirens were preserved, rendering this interesting but unwieldy experiment into the history books. In the first photo of the article, one can see the siren horns peering out of the Lewis's Tower - the second photo is a nice close-up of the "Parmeko" siren, and probably the only detailed photo of it in existence. It was a very unconventional siren compared to what superseded it.
Gent's of Leicester supplied the more populous dual head sirens we see and hear in many wartime films. Very similar sirens were also made by Carter & Co. (Nelson) Ltd. of Nelson, Lancashire. As with the "Parmeko" siren, these were originally made just prior to the outbreak of war in 1939.