This conversation is stupid. For you to develop a tumor, you have to have a multitude of misfortunes occur. First you have to have radiation of substantial energy (I doubt that the energy of a WiFi signal counts) that can penetrate the layer of dead skin cells and keratin just to get to your mitotic (actively dividing) cells to cause damage. Second, the radiation would have to cause a mutation in an exon to actually elicit an effect. Since over 99% of our DNA comprises introns (junk DNA that does not code for anything), this is highly unlikely. Third, we have enzymes whose sole responsibility it is to monitor for DNA damage due to radiation and so these enzymes would have to fail in order for the damage to go unrepaired. Finally, uncorrected DNA damage that leads to cancer is usually stopped by apoptosis (programmed cell death). For the cell not to kill itself, there would have to be a problem in its apoptotic pathway. You are more likely to die by choking on your next slice of pizza than from the added radiation of a WiFi device. Are you going to stop eating pizza?