a-larm' (teru`ah): This expression is found six times in the Old Testament. The Hebrew word so rendered is derived from a verb meaning "to shout" or "blow a horn," as a signal for breaking up camp, starting on a journey or into battle, or in triumphant shout over the defeat of enemies. In a few instances it is employed of a cry of despair or distress. The noun teru`ah translated "alarm" in Nu 10:5 f refers to the signal given the people of Israel to start on their journey in the Wilderness. The passages in Jer (Nu 4:19; 49:2) both refer to the summons for war. The same is true of Zep 1:16.
The law concerning the sounding of the alarm is fully stated in Nu 10:1-10. Here we read that two silver trumpets of beaten work were sounded by the sons of Aaron in case of war and also "in the day of .... gladness" to gather the people together for the various feasts, new moons, sacrifices and offerings.
W. W. Davies