I wiped the doorknobs with disinfectant after returning home.

He gripped the cold doorknob, turned it slowly, and pushed the door open.

That idea was dumb as a doorknob.

When the fireworks started, my grandfather was standing there deaf as a doorknob and didn't notice a thing.

After hours of trying to restart it, the old radio was dead as a doorknob and refused to make a sound.