Set it off have too many meanings, It depends on your application how to use it. " Set it off " is the name of a movie (1996) Dramma, starring: Jada pinkett, Kimberly Elise Set-off (in law), a set-off is a statutory defense to the whole or to a portion of a plaintiff's claim

One meaning is light or ignite some kind of exploding thing: "set off a firecracker" "set off a bomb". In figurative language you can "set off a firestorm" when you do something shocking in public that causes a lot of controversy. "When the governor made terrible comments about poor people, it set off a firestorm of criticism from all sides."