sound the alarm
1. Literally, to activate an alarm. I think I see smoke coming from the warehouse. Someone run upstairs and sound the alarm!
2. To alert other people about something dangerous, risky, or troublesome. A number of top economic advisors tried to sound the alarm before the economic crash, but no policy makers seemed to heed their warnings.
sounding board
A person or group with whom one discusses an idea, plan, or suggestion in order to evaluate its strengths, acceptability, feasibility, practicality, etc. My friend John and I really know each other's skills and interests, so whenever one of us has an idea for a new project, we use the other as a sounding board.
take soundings
To ask questions in order to learn people's opinions about a certan topic. I'm taking soundings to find out what people want to read about in the student newspaper.