Loud noises or light touches wake sleeping humans quickly, yet strong odors—even smoke—rarely wake a person from deep sleep.
Sleep studies at Brown University demonstrated that olfactory processing drops dramatically during deep sleep stages, which is exactly why loud audible smoke alarms save lives.
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Quick Guess: Which sense is least effective at waking a sleeping human?
Verified Answer: Smell
Quiz Question: Which sense is least effective at waking a sleeping human?
Correct Answer: Smell
Because smell won't reliably wake sleepers, fire safety relies on loud audible alarms.
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