English Idiom (英語のイディオム) - Heads up! - (注意喚起)

Heads up is a common expression in English. You may have heard it on a TV show or in a movie. It is usually used in 2 ways.

1. as a noun - an advance warning of something.

Harry: "The boss is in a bad mood today so I would try to stay away from him."

Mike: "Thanks for the heads up Harry."

"I wanted to give you a heads up that I'll be out of the office tomorrow."

"Coconuts may fall from this tree so I wanna give you a heads up."

2. as an adjective - showing that someone is alert and paying attention

"Great passing! That was a heads up play, good job!"

*When your head is down you can't see what's happening around you well.
Your eyes are looking down. 

When your head is up you can see what is happening around you much better. You can see danger coming early, you are alert and paying attention.

Ball is coming! Heads up!