Charles Ellicott Commentary 1 Kings 1:41

"And Adonijah and all the guests that were with him heard it as they had made an end of eating. And when Joab heard the sound of the trumpet, he said, Wherefore is this noise of the city being in an uproar?" — 1 Kings 1:41 (ASV)

When Joab heard—It is one of the many lifelike touches of the narrative that it is the old warrior Joab who, amidst the revelry of his companions, notices the sound of the trumpet, and the acclamation following. Adonijah affects to disregard it.