COMMON If alarm bells start to ring, you begin to be aware of a problem in a situation. It was when the headaches suddenly got a lot worse that alarm bells started to ring. Note: You can also say something sets alarm bells ringing, meaning that something makes you start to be aware of a problem. His absence from work for three days had set alarm bells ringing. Note: You can also say warning bells start to ring. He didn't understand the half of it but warning bells were starting to ring in the back of his mind. Note: You can also say something sets warning bells ringing meaning that something makes you start to be aware of a problem. There was something in the way she spoke that set warning bells ringing in Brak's head.