He is unobservant of his surroundings.

Her unobservantness often leads to misunderstandings.

The detective found an unobserved clue at the crime scene.

He moved unobserved through the crowd.

He moved unobservably through the crowd.

The effects of dark matter on the universe are unobservable.

The existence of dark matter is an example of an unobservable in the universe.

He walked through the crowd unobserving the people around him.

His unobservance of the rules led to his disqualification.

The existence of unobservables in the experiment makes it difficult to draw accurate conclusions.