Infrared
As well as FM Technology, IR has some pros and cons depending on your needs. When confidentiality is needed, IR is recommended, as its signals don’t pass through walls, and/or when there is a need to use more than 6-8 languages in one room. To understand a little bit more, this technology is similar to the one used with remote controls. The transmitter, radiators and receivers should be in the line of sight to work properly.