I set some humming bird food to boil a while back. Got distracted in the other room and smelled smoke. Went back into the kitchen and couldn't see the stove there was so much smoke. Then the smoke alarm went off. Very effective. Took hours to scrub the burn sugar out of the pot and days to get rid of the smoke smell in the house.

Pro tip, always set a timer when you walk away from something on the stove.