We
use it when we want to talk about an event which makes a person realize that
they have to change some kind of negative behavior. Let me give you some ways
to use it in sentences：
I
used to smoke, but when my friend died of lung cancer, it was really a wake-up
call for me. I quit smoking very soon after that.【我以前抽煙，但是當我的朋友死於肺癌時，這真是一記警鐘。之後我很快就戒菸了.】
My
son has been lazy about studying, so he failed his last exam. I hope that will
be a wake-up call for him.【我的兒子已經懶得學習，所以上次考試不及格。我希望這將是一個喚醒他的警鐘.】
