An alarm clock.

注：alarm clock goes off意思是“闹钟响了”，同时go off也有“走开”的意思。

更多英语谜语

The more you take, the more you leave behind. What is it?

What always ends everything?

I'm the part of the bird that's not in the sky. I can swim in the ocean and yet remain dry. What am I?

Which word in the English language becomes shorter when lengthened?