There are many different listening devices available in the market. They are often hidden in daily consumption items (distribution plugs in sockets or extension cords) and can be located anywhere in the room (in the wall, under a picture, in a flowerpot etc.).
Do you know that, today, it is very simple to listen to phone calls and read text messages and viewed mobile data of other people? Not even the loads of mobile apps that are wide-spread and promise "security" of data transmission can really protect you.
In protecting from listening, people frequently forget that data on phone calls can also be disclosed to third parties by any of the participants. It is therefore essential that the risk of listening to a confidential interview by reduced to the people whom the communication concerns.
There are plenty software programs available on the internet through which your computer can be misused. Some of them are masked to look as normal use software, others as applications for downloading films or music but they can actually be viruses or Trojan horses.