空袭警报笛

例句：

1. 1. The school has a system in place to alert students of any impending air raids.
   学校有一个系统，用于通知学生任何即将发生的空袭。
2. 2. During the war, the siren was used to signal the start of an air raid.
   在战争期间，警报器被用来标示空袭的开始。
3. 3. The siren wailed as the bombs fell, warning everyone to take cover.
   炸弹落下时，警报器长鸣，警告所有人躲藏起来。