Numbers 10:4-8

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.

When convening the assembly, however, you shall blow the trumpets without sounding an alarm.

The sons of Aaron, moreover, the priests, shall blow the trumpets; and this shall be a permanent statute for you throughout your generations.