Wifi and Bluetooth are not strong signals, they are very weak signals. And they actually share the same frequency band, so the safe BT and the evil WiFi are the same thing. The only difference is the language they speak. They both operate at 2.4GHz... True, wifi can also operate at 5GHz, but aside from myself a a small set of my friends, almost everyone I know operates at 2.4GHz, and most free/public hotspots are at 2.4GHz. No the frequencies are used for cordless phones too, as well as wireless baby monitors, security cameras, and many more wireless devices. All of the scientific studies show the frequency to be safe. And the power level of the devices is so small I'm at a loss as to the risk of leaving them on. The only radiation that should be of concern is the cellular radiation, since that is almost always right next to your body at some point. And scientific research found that to be safe too, even though it transmits at much stronger signal levels than wifi or Bluetooth.