Numbers 10:2-6

“Make yourself two trumpets of silver, you shall make them of hammered work; and you shall use them for summoning the congregation and breaking camp.

Now when both are blown, all the congregation shall meet you at the entrance of the tent of meeting.

But if only one is blown, then the leaders, the heads of the divisions of Israel, shall meet you.

And when you blow an alarm, the camps that are pitched on the east side shall set out.

Then when you sound an alarm the second time, the camps that are pitched on the south side shall set out; an alarm is to be sounded for them to break camp.