He thought very hard to hear every word under the door.

Maybe he could find the woman who had left the note under his door.

If there was someone out in the hall, they'd see the light under the door.

There wasn't even a line of light from the hall under the door.

If there's a light on in the room, you can see it under the door.

There was light inside, and they could easily see under the door.

"A note came under the door while you were gone."

He could see a thin line of light under the door now.

She could see the thin line the light made under his door.

There was a bar of light under his own door.