What's the scariest sound you have ever heard?

Alarm sound of an ambulance van and the alarm sound of fire engines scarce me a lot. When I am driving a car, when I hear the sound, I just make way immediately for these vehicles to pass.

i was asleep, and there was a moth in the room, it passed by my head and it jus sounded weird, maybe cause i was sleep lol

Oh, I remember that air raid alarm! They used to do air raid drills when I was in elementary school. They would sound the alarm and we would all have to crouch in the hallways with our heads down while that alarm went off... They don't do it here anymore. Do they still have that in India? I think the scariest sound I ever heard was the sound of airplanes taking off after 9/11. I live somewhat close to the airport, and it was very noticeable when no planes flew for a week after the attacks. When they started again, it was a real creepy sound.