alarm/ə'lɑːm $ ə'lɑːrm/

n. a device that warns you of danger

n. [C] 警报；警报器：An alarm suddenly went off. 有个警报器突然响了。

◇a fire alarm 防火警报器

◇an alarm clock 闹钟

构词all + arm （武装）→“让所有人都武装起来”即“警报”

音组-arm/-ɑːm $ -'ɑːrm/

alarm; arm; farm; harm