隔牆有耳

the walls have ears (idiom)

to have; there is / (bound form) having; with; -ful; -ed; -al (as in 有意[you3 yi4] intentional)

ear / handle (archaeology) / and that is all (Classical Chinese)

to separate / to partition / to stand or lie between / at a distance from / after or at an interval of

wall / CL:面[mian4],堵[du3]