be out like a light

1. To be sleeping very soundly. Don't worry, the vacuum won't wake him—he's out like a light. I didn't even hear you come in last night—I was so tired that I was out like a light as soon as my head hit the pillow.

2. To fall asleep quickly. I didn't even hear you come in last night—I was so tired that I was out like a light as soon as my head hit the pillow.

3. slang To be very drunk. Do you remember last night at the bar at all? You were out like a light!