Thanks for the heads up vs Thanks for a heads up

Thanks for the heads-up, Earl.

Okay, thanks for the heads-up about the meeting.

Thanks for the heads-up last night, Janet. It gave me some time to plan my night.

Thanks for the heads up, Artie. See you at the softball game on Friday!

Sorry I missed your call, Mr. Coleman, but thanks for the heads-up.

Although it could be too late to change plans, thanks for the heads up.

Thanks for the heads up. I haven't had time to fix myself up.

Thanks for the heads up on the credit card usage--I didn't know I had spent so much!

Thanks for the heads-up, by the way.

Thanks for the heads-up on the eyewitness who saw the redhead.

"Thanks for the heads up," said the man, after his friend told him that he had jury duty the following week.