How do you turn on the sirens on gta vice city?

Answer 1

You must have assigned the horn button in the game.You need to hit that button short so the sirens will turn on.You can hit the button back to turn the sirens off.Make sure you hit it real short.

Answer 2

You need to hit the button by which you blow horn.For ex you use H for the horn then press the H key fast or what we say hit is and the siren will start.