off
1.
to make a bomb, etc. explode :
A gang of boys were setting off fireworks in the street.
2.
to make an alarm start ringing :
Opening this door will set off the alarm.
3.
to start a process or series of events :
Panic on the stock market set off a wave of selling.
4.
to make sth more noticeable or attractive by being placed near it :
That blouse sets off the blue of her eyes.