i found these sirens on ebay and decided to take a chance on them. The seller's name is robebarr71 and he has some very good deals on these sirens.
They are almost the same size as the DEI siren but are flat on the back so its easier to mount. Which is why i got them.
They also have a totally different sound from the DEI units. I will see about making a recording and putting it up later.
Each siren has a toggle switch to control the volume. I removed mine so i would have a flat mounting surface. The removal is easy. You just desolder the switch and put the power lead where the white lead coming off the switch was soldered on the board. Sorry but i have no pics of that. Its pretty easy to figure out though.
pics of the units.

 

Looks pretty awesome, how does the volume compare to the DEI?

 

i found it louder and more irritating. i will try making a recording tomorrow