"Keep your head on a swivel"

The skipper of my ship used to say "Keep your head on a swivel" every night over the ship's 1MC. (intercom)

When we were at sea, every night at 10 o'clock sharp, the bosun mates would ring the bells, blow the whistle and say, "lights out," then, the skipper would give a talk to the crew regarding the things that went on during the day and about the things that were going on the next day. Whenever he would sign off, he would say, "Keep your head on a swivel."

I always thought it was cool thing to say.

If you've ever watched the movie Apollo 13, you can see our old captain at the end of that movie. He's the tall skinny guy with 4 stripes. I can't remember his name though.

P.S. I was a bosun mate. The nickname for a bosun mate is "boats."