'Sentinel' in the Bible

Now David [was] sitting between the two gates, and the sentinel went up to the roof of the gate by the wall and he lifted up his eyes and watched, and look, a man [was] running by himself.

Then the sentinel saw another man running, so the sentinel called to the gatekeeper and said, "Look, a man running alone." The king said, "This one also [is] bringing good news."

The sentinel said, "I [am] seeing [that] the running of the first [is] like the running of Ahimaaz the son of Zakok." The king said, "He [is] a good man; he will come, for good news."