I was looking at and ad for a product to block cell phone radiation earlier today. The comments posted on it were both positive, and negative. People were debating levels for the front and back as well as a number of other things. Much of the discussion showed a lack of understanding of the phone, and what the shield was.
To start with, a cell phone is a radio. As such, it does put out some RF (Radio Frequency) radiation. This is not as scary as it sounds, because it is not ionizing, or nuclear radiation. There are many forms of non ionizing radiation around us all the time. Light, which we need to see, is a form of radiation. At high levels, RF radiation can be dangerous. An example would be what happens to food in your microwave oven. However the phone puts out a considerably smaller amount.
So there is a demo video with this product. It shows meter readings with and without the case to prove the radiation is reduced. Then goes on to show several happy people using the phone. Here is where the flaw is. The RF signal (radiation) that the phone puts out is not incidental. It is critical to the ability of the phone to connect to the cell sites. If that signal were blocked, as claimed, the phone would not be working. One of two possibilities could be applied to what is shown in the video. Either the case is not blocking anything, which is likely since the edge of the phone is seen, and on many models that is where the antenna is, or the range of the phone has been severely reduced and they needed to be very close to the site for the phone to work.
They additionally claimed to reduce ELF (Extremely Low Frequency) radiation, which would be generally cause by power line magnetic fields. Of course the phone is run on a battery, which is DC and doesn’t produce those fields. Maybe a bit of audio frequency, but probably not significant. You will get much more ELF exposure sitting next to a lamp in your house than the cell phone is capable of producing.
Other examples of products that prey on the lack of understanding of people have been stickers that are supposed to absorb the radiation, or even increase the range of the phone. With sufficient technobabble they sound almost plausible.
There are other devices that put much more energy that cell phones. Two way radios are an example, yet I once saw a person waiting in line to take an Amateur radio test. Someone in the line pull out a cell phone to make a call, and he screamed and ran out the door. There is no shortage of misinformation on the Internet.