The phrase "warning alarm" is used to describe a sound or signal that alerts us to possible danger or a problem that needs our attention. Full definition
Because your blood - sugar level is a key signal for appetite and hunger, this crash triggers major warning alarms in your body. (pages.thealternativedaily.com)
After reading this article, all sorts of red flags went up and warning alarms went off in my head. (religion.blogs.cnn.com)