Found this on Youtube today, which i might say is a very good video of a siren(s) that is a mystery to me. The ones in the background are most likely Whelens but the foreground siren sounds very mechanical but then has a voice to it as well, so probably a electronic that has a recorded mechanical sound. Not sure though....
http://www.youtube.com/watch?v=ZsfKmHXO5Uc
here is another video that looks new as well on youtube
http://www.youtube.com/watch?v=apVIaxVBB8Y