English Proverb: The walls have ears
Often people who commit crimes are caught because they forgot the walls have ears, and someone who was eavesdropping heard them bragging about it in a bar.
You always have to be careful what you say because you never know who is listening or trying to overhear your conversation.
I know that you are not going to commit a crime, but if you are gossiping about someone behind their back, you should make sure that they are not nearby or in the next room.
The walls have ears, and they might overhear you say something that you will regret later.