Sleep with One Eye Open

Stock Phrases about keeping someone on edge during the night.

Film
"Liv: If I were your wedding, I'd be sleeping with one eye open..."
 * Bride Wars

"Lord Darnley: I am one of the finest swordsmen in England, Bothwell.
 * Gunpowder, Treason & Plot

Bothwell: Well, you're in Scotland now *your majesty*!

Lord Darnley: Then sleep with one eye open."

"You have to sleep with one eye open for the rest of your life."
 * Leon.

"I have to sleep with one eye open."
 * Gangs of New York

"Tell him to sleep with one eye open."
 * The Blind Side

"And sleep with one eye open."
 * Ladyhawke

"You sleep with one eye open, son."
 * Mean Machine

"The best thing is to sleep with one eye open."
 * Dance of the Vampires

"I think you should sleep with one eye open."
 * Freebird

"I have to sleep with one eye open."
 * Twin Daggers

"Hey, do yourself a favor, pal. Sleep with one eye open."
 * Gary Unmarried

"What do we do when we are awake?
 * A sort of prayer from Reign of Fire:

Keep two eyes on the sky.

What do we do when we sleep?

Keep one eye on the sky.

What do we do when we see them?

Dig hard, dig deep, go for shelter, and never look back."

Literature

 * In The Hobbit, Smaug does this when he realizes that there is an intruder in his lair. It's not a problem for Bilbo since he can turn invisible.
 * In Scott O'Dell's The Black Pearl, the Sevillano does this while holding a knife in his hand and the pearl in his feet.

Live Action TV
"Simon: [To Jayne] Now, we could circle each other and growl, sleep with one eye open, but that thought wearies me."
 * Firefly episode "Trash".

"Augustus Hill: I gotta share a pod, McManus. I gotta sleep with one eye open."
 * Oz episode "Ancient Tribes"

"Bank Manager: I hope you enjoy your stay in Las Cruces.
 * Bat Masterson episode "High Card Loses"

Bat Masterson: I will now. I have no lock on my hotel room. It takes twice as long to sleep with one eye open."

Music
"I don't really want to be safe
 * Brandi Carlile's song "Shadow on the Wall" contains the lyrics:

It must have been the way I was raised

Sleep with one I open, I say"

"Sleep with one eye open, gripping your pillow tight"
 * Metallica - "Enter Sandman":

"A patient dream that wants to rise
 * Kaleidoscope by Stuart Davis. On YouTube.

I will not close more than one eye"

"But now she sleeps with one eye open, that's the price she'll pay"
 * Florence and the Machine's "Girl With One Eye":

Tabletop Games

 * The Space Marines in Warhammer 40000 can literally sleep like that, thanks to an implant in their brains that allows them to keep one brain hemisphere awake while the other is resting.

Video Games

 * Persona 3: Akihiko says this when SEES decides on investigating a ghost story.