First, you must have a proper meter. To check for magnetic field emissions, an AC Gaussmeter will work. Most AC gaussmeters will have an internal probe. Simply position the gaussmeter on the phone. Note carefully where the meter is positioned. Make a call and watch the readings. Notice the highest and lowest readings, and make a mental note of the "average" reading. Now, insert the magnetic shield, and repeat.

EWG urges the FCC to include third party-produced cases and accessories in its cell phone testing policies to ensure that they do not compromise cell phone function and do not prevent a cell phone from complying with the Commission’s exposure limits. Manufacturers should publish the radiation data for a given phone when used directly next to the body and when used with the cases most commonly sold for a specific model.
The most common effect is heat generation (though non-thermal biological harm has also been demonstrated), which can alter the characteristics of various bodily tissues depending on the amount of radiation present and its ability to penetrate the body. Tissue damage can promote the cellular mutations and increase your long-term risk of developing cancer.
None of the three cases contain metallic parts, which are known to affect SAR, but all increased the user’s radiation exposure. The effect on radiation exposure would likely vary with each of the hundreds of cases on the market, and each would have to be tested individually to come up with an exact measure. The results in Table 1, however, are believed to reflect the range of radiation increases.
George Carlo, PhD, JD, is an epidemiologist and medical scientist who, from 1993 to 1999, headed the first telecommunications industry-backed studies into the dangers of cell phone use. That program remains the largest in the history of the issue. But he ran afoul of the very industry that hired him when his work revealed preventable health hazards associated with cell phone use.
Thus far, the data from studies in children with cancer do not support this theory. The first published analysis came from a large case–control study called CEFALO, which was conducted in Denmark, Sweden, Norway, and Switzerland. The study included children who were diagnosed with brain tumors between 2004 and 2008, when their ages ranged from 7 to 19 years. Researchers did not find an association between cell phone use and brain tumor risk either by time since initiation of use, amount of use, or by the location of the tumor (21).
There's a lot of talk in the news these days about whether or not cell phones emit enough radiation to cause adverse health effects. The concern is that cell phones are often placed close to or against the head during use, which puts the radiation in direct contact with the tissue in the head. There's evidence supporting both sides of the argument.
Some studies have found a possible link. For example, several studies published by the same research group in Sweden have reported an increased risk of tumors on the side of the head where the cell phone was held, particularly with 10 or more years of use. It is hard to know what to make of these findings because most studies by other researchers have not had the same results, and there is no overall increase in brain tumors in Sweden during the years that correspond to these reports.

Leibovich was very careful to point out in our interview that Cellsafe is not claiming that the radiation absorbed by the body during phone use leads to health issues like brain tumours, male infertility or damage to unborn babies. But the Cellsafe website strongly suggests these links. Its homepage (image below) leads with the phrase "You should be concerned!" in an eye-catching red, and there is as much screen real estate on the site dedicated to information about the dangers of radiation, as there is for descriptions of the Cellsafe products. This information refers to "high levels of RF radiation" in several places, but it doesn't say whether this describes radiation from phone use.
Until the FCC establishes testing procedures that fully correspond to real-world cell phone use and reviews its radiation standards to ensure that they are fully protective for all users, including young children, EWG advises phone users to adopt these simple measures to minimize radiation exposure: Use a headset, keep the phone away from the body and text rather than talk.  
While driving, it is best to talk as little as possible on the mobile phone, and in any event, follow regulation 28(b) of the traffic regulations. This regulation stipulates that: “While a vehicle is in motion, the driver of the vehicle will not hold a stationary or mobile phone, and will not use then in the vehicle unless when using a speakerphone; and will not send or read a text message (SMS)”.

I just received this pouch today and it seems to be well-made. I did slide my phone into it (Droid Ultra) and it is snug, but fits. I think my son will also be able to put his ipod in the pouch which is helpful. I mostly bought this because my son puts his phone and ipod in his pocket all the time and I am concerned about the long-term effects of radiation exposure especially so close to his reproductive parts. Hopefully this will provide him with some protection from those elements.
We did not simply measure energy coming from the front of the case which is the area of the case where the phone would be "shielded" from radiation. If we had taken readings with a directional meter, specifically measuring energy coming from only the front or flap cover where the shielding material is, we assume as the manufacturers claim, that we would have seen a drop in the radiation readings.
Introducing, SafeSleeve for Cell Phone. A patent pending, elegant, and stylish solution that seamlessly combines Anti-Radiation and Anti-RFID technology with an impact and scratch resistant case. We've also added an RFID blocking wallet and a built-in stand for peace of mind and convenience. It’s basically the Swiss Army knife of cell phone cases, but with Anti-Radiation Technology instead of that plastic toothpick. 
We began by getting a baseline of ambient RF in the room at the location of our testing. We then recorded a baseline of the cellphone RF while on an active call with no case. And finally, we measured the reduction in that baseline (still on the active call) using a variety of different cases and RF reducing products – all at the same set distance from the phone.
There are few if any references to actual studies in published, peer-reviewed journals that support the claim that Aires, or any other, cell phone shield actually works. The "Researches" page contains a superficially impressive list of sciencey-sounding titles and findings supposedly demonstrating the importance of using cell phone shields, all of them in Russia for some reason.
The peer reviewers did have some quibbles with the study; some wished it could have lasted longer (the rodents were exposed to radiation for two years) to catch later-developing tumors, for example, but others on the panel noted that the longer a rodent lives, the more likely it is to develop tumors regardless of radiation, making it harder to find the signal in the noise. Others wanted the researchers to have dissected the rodent brains more than they did, to seek hard-to-find tumors. But they noted that science is an iterative process; the study wasn’t perfect, but it’s better than anything that’s been done so far.
The papers found that, in male rats, there was “clear evidence” that exposure to cell phone radiation increased risk for a rare type of malignant tumor called schwannoma in the connective tissues that surround nerves in the heart (they found “equivocal” evidence for the same thing in female rats). They also found “some evidence” that the radiation caused malignant glioma—a type of brain cancer affecting glial cells—in the male rats.
The guidelines, issued last week, note that “some laboratory experiments and human health studies have suggested the possibility that long-term, high use of cell phones may be linked to certain types of cancer and other health effects.” These include brain cancer, tumors of the acoustic nerve and salivary glands, lower sperm count, headaches and effects on learning, memory, hearing, behavior and sleep.
To answer this question, Lloyd uses an analogy of “smoke and a chimney” to explain how a Pong case works.  It is unfortunate — given Lloyd’s personal experience with electrohypersensitivity and his straightforward knowledge of how to measure RF exposure — that pure “smoke and mirrors” clouded his better judgement when reviewing the Pong case for cell phone radiation safety.
Could you please provide me with evidence that non-ionizing radiation is damaging to humans? In another post illustrating the threats of non-ionizing radiation you have said that this radiation is damaging to children, and link an article by the American Academy of Sleep Medicine. However, this linked page contains no mention of non-ionizing radiation, and instead suggests that children are simply addicted to use of mobile phones, thus using them instead of sleeping. You also provided a link to a PubChem page on the negative effects of this radiation, but this page appears to no longer exist.
Of course, scientific seesawing like that doesn’t provide a lot of clarity or confidence for the 90 percent of American adults and roughly 80 percent of teens who report having a cell phone. So how concerned should you be about cell-phone radiation? Consumer Reports’ health and safety experts conducted a thorough review of the research and offer some guidance.

A cellular phone is basically a radio that sends signals on waves to a base station. The carrier signal generates two types of radiation fields: a near-field plume and a far-field plume. Living organisms, too, generate electromagnetic fields at the cellular, tissue, organ, and organism level; this is called the biofield. Both the near-field and far-field plumes from cell phones and in the environment can wreak havoc with the human biofield, and when the biofield is compromised in any way, says Dr. Carlo, so is metabolism and physiology.
Some products ( for example) are tested using a piece of shielding material in a laboratory test jig. These tests legitimately show the amount of radiation which penetrates the shield, but results will be very different when compared to putting a small amount of the same shield on a large transmitter like a cellphone. Remember, the entire phone radiates. Placing a small amount of shielding, even if it is an effective shielding material, only shields that small area at best. Think about this analogy: no light will penetrate a penny as it is a very effective light shield, but it is silly to think that holding a penny up to the sun will put you in darkness.
Don’t be mislead by a common misconception started in the 90′s that wired headsets, that the headset that came with your cell phone is a safe alternative to placing a phone to your head.   This is simply not true at all! Ordinary headsets use a wire to deliver sound to an electronic earpiece that can deliver electromagnetic radiation into your head directly through your ear canal.
The government’s policies must change. Cell phone users should make their voices heard to prompt the FCC and manufacturers of cell phones and cases to ensure that these accessories never increase and, to the extent possible, decrease, users’ radiation exposure. At minimum, the FCC must take cell phone cases into consideration when it updates its standards to ensure that the use of a case will not expose people to more radiation than its legal SAR limit.  
Our homemade demonstration of all the cases uses a working phone. Not the shielding material by itself, but the actual "shielding" SafeSleeve, Pong, Reach,  Vest, ShieldMe, and Defender Shield cases. First we get RF power density measurements from a phone that's on a call and then, in the same location, within minutes of the first reading, we place the same phone as it's engaged in a call into each case and we take additional reading with the meter.
The authors of these studies noted that the results were preliminary and that possible health outcomes from changes in glucose metabolism in humans were unknown. Such inconsistent findings are not uncommon in experimental studies of the biological effects of radiofrequency electromagnetic radiation in people (4). Some factors that can contribute to inconsistencies across such studies include assumptions used to estimate doses, failure to consider temperature effects, and lack of blinding of investigators to exposure status.