Someone keeps leaving notes on my door… but I live on the 12th floor

I live alone on the 12th floor.
No balcony.
No fire escape.
No way to reach my door except through the hallway.

But every morning, I find a note taped to the outside:

“I saw you.”
“Don’t close your curtains.”
“You look different when you sleep.”

Last night, I stayed awake and watched the peephole.

At 3:17 AM, someone tapped on the door.

But the hallway was empty.

The note this morning said:

“Stop watching.”