do you really want or need to spy? By listening through a wall, you are about to spy on another person and violate private conversations. This raises big legal and ethical problems. Before acting, seriously ask yourself if you want to do it. Is it worth the risk?  The situation is important. In England, for instance, a man rescued his elderly neighbor from a robbery by listening through the wall with a glass. In his situation, spying was definitely justified. Things are rarely so clear cut, however. You should probably not act if you have any doubts about the situation. If you decide to go ahead, make sure that you know the possible consequences of your actions. Eavesdropping means to overhear, record, magnify, or transmit any part of a private conversation without the consent of at least one person involved. Be aware that states have laws against eavesdropping. By spying you may well be breaking the law; you might even be violating the law by possessing a device for spying.  Your state may have a “one party consent” or “two party consent” law. One party consent means that it is illegal to eavesdrop unless you have the consent of at least one of the people engaged in a private conversation. In two party consent you must have permission from both parties to listen, record, or amplify their communication.  Take the state of Michigan. Michigan has a two party consent law – you must have permission from all parties in order to “overhear, record, amplify, or transmit any part of a private discourse.” This applies even in your own home. Eavesdropping there is also a felony. What happens if you eavesdrop and someone finds out? What could happen to you? This is a good question and you should consider all of the possible outcomes, which in many cases are severe.  In Michigan, the penalties for illegal eavesdropping are up to 2 years in prison, up to $2,000 in fines, or both. In California, eavesdropping is either a misdemeanor or felony. As a misdemeanor you face up to 364 days in jail and a $2,500 fine; as a felony,...

TL;DR in Vietnamese:
Tự hỏi bản thân xem có phải bạn thực sự muốn hoặc cần nghe lén không? Nhận thức về luật nghe lén. Cân nhắc tất cả hậu quả tiêu cực.