It is hard to tell the difference in when the siren is wailing but the start up has a raspy tone to it that give away the fact that it's electronic vs the smooth wind up of a mechanical Q
I've seen a EQ2B on a fire truck from I think it was West Covina. I was over at the Diamond Bar City hall while they were having a fire fighter's meeting and there were apparatus from several neighboring cities parked in the lot. I noticed one of the Qs looked flatter than normal (it was mounted to the front bumper) so I walked up and peeked through the grill. Instead of the chopper, they had a BP200 speaker behind the grill
http://www.fedsig.com/products/index.php?id=120 The controller knob itself was mounted on the center console in the cab.
One fire fighter who was walking by saw me looking and said "Oh, that's the new electronic siren but we still prefer the mechanical "growlers"
I didn't get a chance to hear it in person since all of them left with only airhorns blasting but no sirens.
BTW, I wonder if the entire Chicago Fire Department has EQ2Bs. I can't see the controls because there's a boot in the way but it does do the wind up and down all by itself.
http://www.youtube.com/watch?v=xigsveMK_VA