I’m sure you are familiar with the phrasal verbs turn on and turn off. There is, however, another phrasal verb, go off, which can be quite confusing to ESL students.

When talking about an alarm, go off  means to start working (by making a loud noise).

I set my alarm to go off at 7am this morning.

I woke up when the smoke alarm went off.

I was late to class because my alarm didn’t go off.

When your alarm goes off, you should turn it off quickly so it doesn’t wake anyone else up.

Go off can also be used to talk about a gun firing or a bomb exploding.

While he dropped the gun, it went off.

Don’t play with the gun, it might go off.

The bomb went off in the middle of the night.

Finally, go off  on can be used idiomatically to mean “become very upset and start yelling”.

His wife went off on him because he had forgotten her birthday.

The boss went off on his secretary for being late to work again.