Walls have ears

Several years ago, a news channel in Europe reported,“In the smart city of Santander the walls have ears.”Did the walls in this Spanish（西班牙）city have“real” ears? Researchers planned to use acoustic infrastructure to improve the lives of Spanish people. For example, this smart system could measure the noise levels on the streets and change the traffic lights so that an ambulance could get to the hospital faster. Although some people were concerned about privacy, researchers responded that no personal conversations would be recorded. 

Why do people worry that walls have ears? When someone tells you that the walls have ears, he or she wants to warn you to be careful of what you say because other people, especially enemies, might overhear you. 

Don’t talk about our business plan in this room. Walls have ears. 

An ancient Greek story is said to be related to the origin of this idiom. Over two thousand years ago, Dionysius, the cruel tyrant of Syracuse, built a cave in the shape of an ear to connect the rooms of his palace. This could allow him to listen to the conversations in other rooms. 

The idiom appeared in a French-language manual,“The French Alphabet”, as early as in 1592. 

“The walles may have some eares ⋯⋯ Les murailles ont des aureilles.” 

Interestingly, a similar version of this idiom is found in the Chinese language ——“隔牆有耳”. However, the Chinese version comes from an ancient Chinese political and philosophical article,“Guanzi”（《管子》）, written nearly 3,000 years ago.