The most ominous-sounding siren I've heard is the HOR Super Sirex, a gigantic, 50 Hp. siren with a slow windup and a 7/10 ratio (the notes G and C#, give or take). This is a flatted 5th interval, not a minor 2nd, which would have one tone a semitone above the other. I don't believe that a minor 2nd ...