'Watchman' in the Bible

Now David was sitting between the two gates: and the watchman went up to the roof of the gate to the wall, and lifted up his eyes, and looked, and, behold, a man running alone.

The watchman cried, and told the king. The king said, "If he is alone, there is news in his mouth." He came closer and closer.

The watchman saw another man running; and the watchman called to the porter, and said, "Behold, a man running alone!" The king said, "He also brings news."

The watchman said, "I think the running of the first one is like the running of Ahimaaz the son of Zadok." The king said, "He is a good man, and comes with good news."