Wifi signals have an extremely low wavelength, similar to that of cosmic background radiation. Wifi signals are still higher than other more dangerous wavelengths, like ultraviolet light or X-rays. Instead, Wifi signals are at a level akin to other higher-wavelength signals - microwaves, infrared, and radio waves.

Baby alarms
Cordless phones
R/C cars
Bluetooth headsets
Security alarms
Remote controls

These are the things that operate in the same radio frequencies that Wifi does. The intensity of a wifi signal is about 100,000 times less intense than a microwave oven. While a microwave does things like shoot high-intensity rays in a small, confined space, Wifi routers operate at comedically low voltages and broadcast in all directions. Furthermore, like all radio waves, the signal drops of fast - very, very, very fast.

There have been hundreds of attempts to find out whether Wi-Fi routers or, more importantly, mobile phones represent a health risk. All we can say is that there is no known risk from Wi-Fi. After that, there's the problem of trying to prove a negative.

If you're actually afraid of your electronics doing damage to you, throw your phone away. Right now. You're going to get as much radiation from a 20 minute call as you would from 2 years' worth of sleeping next to a WiFi router or receiver..