The so-called WiFi networks are another source of electromagnetic fields which can be extremely harmful.
The EM fields of a WiFi system depend on the number of devices, the number of antennas installed, the dimensions and the geometry of the rooms and buildings, the materials in the walls and floors and so on。
We have had some very bad health symptoms due to WiFi systems in offices. All over the world much people that works inside buildings where WiFi has been installed is getting sick.
WiFi communication networks create electromagnetic fields in the microwave frequency bands。 At these frequencies the wavelength is of 10-30 cm so in a room where the WiFi antenna is installed the distance from the antenna is only few wavelengths。 The electromagnetic field created by an antenna in this region is very different from the field coming from a transmitting antenna placed at about 100 m, like the cellular telephony towers。
The first difference is that in the near zone the field intensity is much greater than the one calculated with the inverse square law for the wave power。 The inverse square low is correct only in the far zone of the electromagnetic field。 Furthermore in the indoor systems there are many objects near the antenna so the simple free space model is not correct。 An object, expecially a metal rod or slab, will capture and radiate again the electromagnetic field thus bringing the source nearer to the user。
In a typical indoor WiFi system people are exposed to the near field of the antenna.
In some particular cases, like buildings made in great part of metal, the rooms will become the equivalent of a microwave oven, of course the intensity is not enough to make water boil but is far greater than what it was expected in open space.
There's no need to harm workers and students with such things, computer networks can work very well through cables, and cable based office networks are also faster, more reliable and more secure.
Unfortunately even wireless mouse and keyboard are not good for health. The level of electromagnetic fields generated by these small devices varies much between particular models, and you don't know how strong their emission are until you have bought them and used them for some time.
Some harmful emissions are coming even from non-wireless keyboards and mouses, but usually they are low enough, unless you put the keyboard on your lap.