ear to the ground
ear to the ground {n. phr.}, {informal}
Attention directed to the way things are going, or seem likely to go, or to the way people feel and think.
The city manager kept an ear to the ground for a while before deciding to raise the city employees' pay.
Reporters keep an ear to the ground so as to know as soon as possible what will happen.
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Source: A Dictionary of American Idioms