to cause something to start happening, especially suddenly or unexpectedly.
The smoke set off the fire alarm in the kitchen.
A: Why did the dogs start barking? B: I think the fireworks set them off.
Loud noises can sometimes set off anxiety in people, especially if they are sensitive to sound.
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'.
Tell it apart
The smoke set off the alarm.
triggered it
We set off early to beat the traffic.
began the journey
Use 'set off' for things like alarms, reactions, or events, not for starting planned activities.'Set off' here means to trigger something, not to physically leave a place.
to make something look more attractive or noticeable by being different from it, especially through contrast in appearance or qualities.
The bright blue cushions really set off the neutral tones of the living room.
A: That necklace looks amazing on you! B: Thanks! I think the green stones really set off my eyes.
The architect chose dark window frames to set off the light stone façade, creating a striking visual effect.
Common mistake
✗That scarf sets off with your eyes.
✓That scarf really sets off your eyes.
'Set off' takes the object directly (no 'with') — it means 'makes it look better by contrast'.
Tell it apart
The lighting sets off the artwork.
makes it stand out flatteringly
The lighting set off the alarm.
triggered it
This sense is used in descriptive and evaluative contexts, often about appearance, design, or style. It is neutral in register and common in both spoken and written English when discussing aesthetics or qualities.Unlike the B2 sense of 'set off' meaning 'to trigger' (cause something to happen), this sense is figurative and refers to making something stand out or appear more attractive by contrast, not to initiating an action or event.