Short waves. Pathway of light directly on the production of cheap, easy safe to trap the signal cannot pass through the object, you can install the Infrared. In an adjacent room.
The passage of the light wave straight cheap, easy to produce safe to trap signals can not penetrate the material. Infrared allows installation In the office next door
Short wave light path, a straight line, cheap, easy to produce safe to jamming can not penetrate through the object. It can install Infrared room work together. "