Charles Ellicott Commentary Numbers 10:5

"And when ye blow an alarm, the camps that lie on the east side shall take their journey." — Numbers 10:5 (ASV)

When you blow an alarm. — The word teruah, alarm, is supposed to denote a loud and continuous blast, by which the signal for the moving of the camps was distinguished from those which were used for summoning the congregation, or of the princes (Numbers 10:7). In the former of these cases, some suppose that both trumpets were blown, and in the latter, only one (Numbers 10:4 and Note. Compare to Lightfoot’s Temple Service, Numbers 7:5; Numbers 7:2).

The fuller directions respecting the order in which the camps were to break up are given in Numbers 2. Here, the order of the eastern and southern camps only is prescribed. In the Septuagint, however, we read this: And you shall sound a third alarm, and the camps pitched by the sea (i.e., westward), shall move forward; and you shall sound a fourth alarm, and those who encamp toward the north shall move forward; they shall sound an alarm at their departure.