I'm making shit up because I recognized a smell without having to see it was there? If I smell dog shit and check the area and find, you know, dog shit, does finding the dog shit invalidate the scent?
I mean, you just can't be this dumb, can you?
Because, dumbass, a smoke detector picks up carbon monoxide and warns everyone in the building before the smoke can reach every room. Or, if you're sleeping and a fire starts, the noise is loud enough to wake most people. I've smelled smoke from burning food from completely a completely different room without even knowing anyone was cooking. That doesn't magically make smoke detectors pointless, it means I have a sense of smell and can figure out what something is without having to see it.