You may well have seen a list of "Top radiation producing mobile phones" or on the other hand "Safest mobile phones", in each case the phones in question being ranked by their SAR rating. (SAR stands for Specific Absorption Rate and is intended to be a guide to how much radiation you will absorb if you use that phone.) Perhaps, after seeing this list, you will wonder "Why on earth do they let people buy the ‘dangerous’ phones? Surely they should only have the ‘safe’ ones on the market?"
But it is not as simple as that. SAR ratings are just a relative number. They do not denote a phone that is ‘safe’ or even one that is ‘dangerous’. They are a very imperfect guide to the relative amount of cell phone radiation you will absorb with the phone at a set distance from your body and using a set strength of signal. In other words, under controlled laboratory conditions. Out in the real world, the amount of radiation you would absorb using one of these phones would be very different. That is because the factors that govern radiation absorption can have a far greater effect on how you absorb than the SAR number of the phone will.
The most important of these factors is distance between you and your phone. The radiation signal created by the phone starts off very strong, but declines exponentially with distance. At one centimeter from your body it is high; at one metre it is far lower; at ten metres it has declined dramatically. This is why where you keep your phone is of more consequence than its precise SAR rating. Any phone on the market is dangerous if kept right next to your body. Any phone on the market is safe if kept ten metres away.
If you do keep your phone near your body, the only safe option you have is to keep it in an anti-radiation case.