danger signal

例句：

1. 1. The police are looking for a dangerous signal in the area.
   警方正在该地区寻找一个危险的信号。
2. 2. The doctor gave me a warning sign that I should see a specialist.
   医生给我一个警告信号，让我去看专家。
3. 3. The fire department received a dangerous signal from the smoke detector.
   消防部门收到了来自烟雾探测器的危险信号。