'To set off,' could mean to trigger something, like an alarm. Example: The burglar set off the alarm by breaking the window.' It could mean to cause something, like an explosion. Example: The timer set off the bomb. or Mixing of the liquids set off a chemical reaction. Another meaning of 'to set off,' is to leave. Example: Emma and Rob set off for New York - meaning they left for New York. 'To set off,' could also mean to make angry. Example: 'Their bad driving set me off.' As you probably noticed, it all depends on context. Perhaps you were thinking of an example?

to get away: 1. to escape, - the police chased the thief but he was too fast and got away; he got away from the police. 2. to depart - the freeway will be choked with cars as people return home tomorrow; let's try and get away early in the morning and avoid the traffic. We got away before 7am and missed the heavy traffic. Set off: 1. to depart - you could replace "get away" with "set off" in the example above. 2. to cause something to begin - when the car crashed into the petrol station, it set off an explosion which destroyed all the buildings; when her mother heard about her new boyfriend, it set her mother off again!

'To get away from,' means to escape. Example: 'She was able to get away from the kidnapper.' 'I need to get away from it all,' - means I need to escape from everything that's going on.' You could also say 'get away from me,' and this means, go away or leave me alone. 'To get away with,' means, to avoid getting punished for doing something. Example: The children were able to get away with not cleaning their rooms. He was able to get away with cheating on the test.