She had not even noticed his approach, or the touch of the helmet.

The dog's head was bent low, too concerned for the raw meat at its feet to notice the man's approach.

Intent upon their purpose the three did not notice his approach.

There was no sign that anybody had noticed her approach.

The man didn't have to worry about anyone noticing his approach.

None of the three on the ship had noticed our approach, and we were quite close to her before they discovered us.

He hadn't even noticed their approach in his mirror.

So much so that she didn't notice the young man's approach until he was right next to her.

We are so focused on each other that we do not notice its approach.

No one had noticed his approach, but that was not unusual for the degree of concentration involved.