My rescued GSD, Killian, howls when he hears sirens: police, ambulance, fire, security systems and tornado. On the day we adopted him, on the drive home, an ambulance drove past and he started howling!!!! Even on our walks, if he hears the police, he'll howl and walk! We get a kick out of it. Shiloh isn't very good at it. She howls and barks at the same time.