set off — trigger something
phrasal verbB2IELTS 6+neutralcommon
to cause something to start happening, especially suddenly or unexpectedly.
Say it like a native
Textbook The smoke activated the fire alarm.
Native The smoke set off the alarm.
'Set off' is the everyday verb for triggering something; 'activated' is technical.
Pattern: set off [noun]
In use
- The smoke set off the fire alarm in the kitchen.technology
- Loud noises can sometimes set off anxiety in people, especially if they are sensitive to sound.IELTS speaking
Common mistake
✗ The burnt toast set off to the alarm.
✓ The burnt toast set off the alarm.
'Set off' takes the thing triggered directly — no 'to'.
Common collocations
set off + trigger— the alarm, fireworks, a chain reaction, a debate
Don't confuse it
'Set off' here means to trigger something, not to physically leave a place.
Related
- set off (start a journey) — Another meaning of 'set off' is 'start a journey'; compare the examples to keep the meanings separate.