a 10-4 - A 10-4 is when you are telling someone you heard them, like

A 10-4 is when you are telling someone you heard them, like in a loud place or over a bad connection.

He shouted, "10-4, I heard you over the loud music!"

She said, "10-4, I heard that from my phone."

He yelled, "10-4, I heard you from my truck!"