Our sense of smell switches off when we sleep
While we're asleep, our sense of smell temporarily is turned off. It is also the last thing to activate once you wake up. When there's a fire or a gas leak, sound would disrupt your sleep way before your sense of smell. This is according to a study done by Brown University when they compared their sense of smell when they're awake and when they're a sleep. They also tested the participants during each stage of sleep.