1. Pay attention to the phone when talking on the phone
Pay attention to sound changes, silence, intermittent sounds or other unfamiliar sounds. Amateur eavesdropping equipment often produces such interference.
2. Listen to the phone when you are not making a call
Pay attention to the sound coming from your home phone. If you hear the above noise, it means that the phone may be bugged. Some bugs use amplifiers to eavesdrop on people within a certain range.
3. Check the locks
If they suddenly become loose or have been inserted, they may have been manipulated recently.
4. Pay attention to things in your home or office
New things equipped with bugs are often placed in places where the victim is unaware. Common new items are radios, alarm clocks, sprinklers, picture frames, and light bulbs. Also be aware of gifts that may contain eavesdropping equipment. Common eavesdropping gifts are power adapters, pagers, pens, water dispensers, calculators, briefcases and CD players, etc.
5. Be aware of interference signals
Be aware of any interference with radio or television signals in your car, home or office. Listening devices emit signals that interfere with radios and televisions.
Precautions against eavesdropping at home
When the phone is hung up, the sound comes from the phone receiver. This is usually caused by hook switch bypass, which turns the phone receiver into a bugging receiver (and speaker). It's possible that someone is within a few meters listening to what is said or monitoring everything that is done.
The phone often rings, but no one speaks when it is picked up, or the sound is very weak, or a high-pitched tone is heard for a while, and then turns into a buzzing sound in the blink of an eye. This is a sign that a slave device or line extender is being used on the telephone line. This is also a key sign that a harmonica or remote-controlled bug is being used.
When the phone receives control (by using an external amplifier), a tone can be heard. Listen to the phone lines. If you hear a faint solid two-tone tone, it means someone is using a slave listening device on their own (or a neighbor's) phone line to leak secrets.