The latest fun fact claims we have no sense of smell when we are asleep but I am sure I have heard of people waking when they smelt smoke.

According to the 'Sense of Smell Institute', various other sources I looked at, and my own experience, that is not true. This is part of an article which delved deeply into smell - don't know if that sounds right. It is also proven that people without the ability to hear have in fact been awakened instead by a smell that alerted them to danger. That makes sense since they have heightened responses in order to compensate for a lack of one function.

"Is our sense of smell active while we
sleep? Dr. Peter Badial has discovered that
our sense of smell definitely does function
when we're asleep. Scientists
found that the olfactory receptors were
stimulated when an odor was present
and that the brain was receiving the
odor stimulation. Even people who
reported that they couldn't smell the
test odor while they were awake were
unconsciously affected by the odor
while they were sleeping."