You asked us, "Why does my dog howl at sirens?" and that question has been a head-scratcher for a while, almost as if sirens have an evil power over most dogs.
Their heads start to go up, their doggy-lips start to purse, and out it comes, as if they have no control over it.
For a long time, the explanation was simple, that it hurts.
Dogs' hearing is so much more sensitive than ours ... that a sound that's just irritating to us must be excruciating for them, but if you've ever seen a dog howling along with a fire truck, they don't seem to be unhappy, and in fact, they look pretty pleased with themselves.
Canine science points us in another direction, to dogs' cousins and ancestors, the wolves.
Wolves don't bark to communicate, they howl. Hear a wolf howl. What's that, girl? That seems to translate to "I'm lonely, friend" or "Go away, stranger."
These wolfish responses are also hardwired into your dog's head, so given the smug aftermath of a good howl, I'd put my money on the "Go away" explanation of your dog's big yowl.