Any really strong stimulus can wake you. I am sure that if you had had a really traumatic experience related to a smell, such as having nearly been burnt to death by a tar fire, then the smell of hot tar might wake you.

Also, some strong-smelling gases have effects that go beyond smell. A faceful of ammonia, acetic acid fumes, sulphur dioxide or the like certainly would wake you, coughing and choking, as surely as a blow.

Very often people sleep through the smell of smoke and die in house fires. Get a smoke detector and a carbon monoxide detector.

The mention of carbon monoxide in this case is not really relevant. Carbon monoxide does not smell, has no taste and is slighltly lighter than air. Recently some youths were killed because they slept above the garage in which they had left their car running.

Any stimulus that is perceived as strong, as Jon-Richfield correctly states, can wake a person up. People who like coffee can be awakened by the smell of coffee. If you shine a strong light in the face of someone who is sleeping they will probably wake up.

But it does not have to be an external stimulus. Many people wake up when they have to go to the toilet at night, probably because the body generates a strong stimulus to wake up.