But researchers can make some judgments about the potential for harm based on how WiFi and similar technologies work, as well as on how people tend to use their devices. Those factors do provide some reasons to think that WiFi and Bluetooth devices may be less of a concern, says Leeka Kheifets, Ph.D., a professor of epidemiology at the UCLA School of Public Health who has studied the potential health effects of low-level radiation.
Our recommendation is to reduce your exposure from wireless sources. We advocate what’s referred to as the Precautionary Principle. Basically, this means that because there’s research, lots of it actually, saying the energy that powers our cellphones (RF radiation) could be causing health concerns like tumors and cancer. We ought to take care when using our cell phones and all devices that emit RF, using them mindfully.
Moving the meter around the case, we detect readings on the side, back and front of the case. We use the multi-directional TES 593 meter which measures 10 MHz to 8GHz. We use the unit of micro-watts per square centimeter, which looks like this little symbol: μW/cm² and we use it on the max setting which shows the maximum measured value. In non-science speak: the highest level of RF we see, which could be from the back the side or the front. 
While that’s all scary as heck, I think it’s everything we don’t know about EMF exposure that scares me the most. That, and how seldom EMFs are discussed. If it hadn’t been for my dear friend August Brice, a Tech Wellness Advocate, I don’t think I would have ever considered the safety hazards associated with everyday cell phone use. Or had any knowledge of the subject whatsoever. Let’s be real, this topic has certainly never appeared in the trending tab on Twitter, and I’ve yet to see it spark a viral video.
Foster was Moulder’s coauthor on that 2013 review of Wi-Fi’s health effects. He says that, based on our current understanding of radio wave strengths and risks, world health authorities have set safety standards for all devices and appliances that emit electromagnetic radiation—from phones and microwaves to your car’s keyless entry fob. “The exposure you get from your Wi-Fi router is orders and orders of magnitude below those safety limits,” he explains.
BACKGROUND: Dental amalgam is composed of approximately 50% elemental mercury. Despite concerns over the toxicity of mercury, amalgam is still the most widely used restorative material. Wi-Fi is a rapidly using local area wireless computer networking technology. To the best of our knowledge, this is the first study that evaluates the effect of exposure to Wi-Fi signals on mercury release from amalgam restorations.

Repeated Wi-Fi studies show that Wi-Fi causes oxidative stress, sperm/testicular damage, neuropsychiatric effects including EEG changes, apoptosis, cellular DNA damage, endocrine changes, and calcium overload. Each of these effects are also caused by exposures to other microwave frequency EMFs, with each such effect being documented in from 10 to 16 reviews. Therefore, each of these seven EMF effects are established effects of Wi-Fi and of other microwave frequency EMFs. Each of these seven is also produced by downstream effects of the main action of such EMFs, voltage-gated calcium channel (VGCC) activation. While VGCC activation via EMF interaction with the VGCC voltage sensor seems to be the predominant mechanism of action of EMFs, other mechanisms appear to have minor roles. Minor roles include activation of other voltage-gated ion channels, calcium cyclotron resonance and the geomagnetic magnetoreception mechanism. 

We really do not recommend any kind of chip, guard, anti-radiation "filters" or incomplete shielding case because honestly, how could they NOT provide a false sense of security? Folks could believe these products make them “invincible” against radiation so they are comfortable holding the case right up to their heads-and the radiation seeping from the back and the side of the phone case is in very close proximity to their precious brains. Oh no!
And yet, a lot of people do use these, including people I know and respect. I see people on the subway playing Candy Crush, the cover of their folio-style wallet case folded back, all of their cards just flapping in the wind. And don’t just take my word for it: The Silk iPhone wallet case has nearly 2,000 reviews on Amazon with an average score of 4.5 stars. People not only use these cases—they love them!
An analysis of data from NCI's Surveillance, Epidemiology, and End Results (SEER) Program evaluated trends in cancer incidence in the United States. This analysis found no increase in the incidence of brain or other central nervous system cancers between 1992 and 2006, despite the dramatic increase in cell phone use in this country during that time (22).
The very next day, a livid Tom Wheeler began publicly trashing Carlo to the media. In a letter he shared with the CEOs, Wheeler told Carlo that the CTIA was “certain that you have never provided CTIA with the studies you mention”—an apparent effort to shield the industry from liability in the lawsuits that had led to Carlo’s hiring in the first place. Wheeler charged further that the studies had not been published in peer-reviewed journals, casting doubt on their validity.10
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All values were far below International Commission on Non-Ionizing Radiation Protection’s (ICNIRP) reference values, but most mean levels measured were above the precautionary target level of 3–6 µW/m2 as proposed by the Bioinitiative Report ….however the ICNIRP guidelines are based on short-term heating (thermal) effects, and are therefore not relevant to decide on the appropriateness of long-term exposure.

I really want to caution you to be careful of any "expert" or EMF blogger recommending anti-radiation filtering cases, stickers that attach to the phone or necklaces to "ward off" EMF.  I get it, when I first realized 25 years ago that I was sensitive to electromagnetic energy and then later, when I understood that without a doubt, man made electromagnetic radiation has a biological effect on my body, I wanted an easy fix.  I tried the shielding materials and cases and I just did not feel any better.  Then I bought meters to see if the energy changed and I actually noticed what the California Department of Health now says and it's what the FTC and FCC post warnings about:  "Some shielding materials can make exposures worse". So please, be careful and read on for what you can do to avoid electromagnetic radiation exposure.

The energy of electromagnetic radiation is determined by its frequency; ionizing radiation is high frequency, and therefore high energy, whereas non-ionizing radiation is low frequency, and therefore low energy. The NCI fact sheet Electromagnetic Fields and Cancer lists sources of radiofrequency radiation. More information about ionizing radiation can be found on the Radiation page.
In those cases, however, there are two important things to note. The person exposed to the non-ionizing microwave radiation would be exposed to a very high power dose at a very close range. The magnetron in your average consumer microwave produces about 700 watts of microwave energy, and that microwave discharge is safely contained within the body of the microwave thanks to proper shielding. Even if the microwave was malfunctioning and the shielding was beginning to fail, you wouldn’t even feel anything standing in the same room as the device.
It’s unfortunate, but kids are a clumsy lot, and even the best behaved little ones will often knock their precious phone flying across a room. With that in mind, it’s often worth making sure that their phone can take those sorts of knocks and come out without much of an issue. The Nokia 6.1 is a such a phone. It bucks the recent trend for glass with an all-metal build that feels extremely solid. It’s not exactly a rugged phone, but it should be able to take some accidental drops and knocks better than a glass phone.

Cancer is the obvious start. An early concern with mobile technology was clusters of the disease around those living near phone masts. One study in Israel found a 4.5-fold increase in cancers of all kinds in the immediate vicinity of a mast (Int. J. Cancer Prev., 2004). In 2009, a Korean team of researchers carried out a pool analysis of the results of 23 studies, which involved almost 38,000 subjects.