A 2005 study in the International Journal of Cardiology found that mobile phones may have "adverse effects" on pacemaker functions under certain conditions.  According to the US Food and Drug Administration (FDA), radiofrequency energy from cell phones can create electromagnetic interference (EMI) that may disrupt the functioning of pacemakers, especially if the cell phone is placed close to the heart.  The American Heart Association includes cell phones on its list of "devices that may interfere with pacemakers." 
The U.S. Food and Drug Administration (FDA) notes that studies reporting biological changes associated with radiofrequency radiation have failed to be replicated and that the majority of human epidemiologic studies have failed to show a relationship between exposure to radiofrequency radiation from cell phones and health problems. The FDA, which originally nominated this exposure for review by the NTP in 1999, issued a statement on the draft NTP reports released in February 2018, saying “based on this current information, we believe the current safety limits for cell phones are acceptable for protecting the public health.” FDA and the Federal Communications Commission share responsibility for regulating cell phone technologies.
The device comes in a variety of forms ranging from the $39 Aries Shield ("a silicon based micro processor that ... decomposes oscillations of electromagnetic fields") to the $249 Aires Defender Utility (which "has two next generation 9 core silicon based micro processor (sic) that provide universal protection from electromagnetic smog of the broadband frequencies").
We can’t stop people from misleading others for profit, but we can respond to their nonsense. We’ve received more than a few letters here at How-To Geek from concerned readers asking if they should turn off their wireless equipment when not in use, or get rid of it altogether. So we’ve decided to add a reasonable voice to the conversation so, hopefully, people will find this and breathe a much deserved sigh of relief.
Wheeler’s tactics succeeded in dousing the controversy. Although Carlo had in fact repeatedly briefed Wheeler and other senior industry officials on the studies, which had indeed undergone peer review and would soon be published, reporters on the technology beat accepted Wheeler’s discrediting of Carlo and the WTR’s findings. (Wheeler would go on to chair the Federal Communications Commission, which regulates the wireless industry. He agreed to an interview for this article but then put all of his remarks off the record, with one exception: his statement that he has always taken scientific guidance from the US Food and Drug Administration, which, he said, “has concluded, ‘the weight of scientific evidence had not linked cell phones with any health problems.’”)11
This study aimed to examine the therapeutic effects of a 100 Hz pulsed electromagnetic field (2 h/day for 60 days) on the reproductive systems of male Wistar rats (70 days old).The results showed significant increases in caspase and creatine kinase and significant decreases in testosterone and melatonin in the exposed groups. This finding emphasizes that reactive oxygen species (a potential inducer of cancer) are the primary cause of DNA damage. However, pulsed electromagnetic field exposure relieves the effect of microwave exposure by inducing Faraday currents.
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In a separate study by the same Swedish team, they found more than seven times the risk among people using a cell phone more than 20 years and 6.5 times the risk for long-term users of cordless phones. As expected, most of the gliomas and acoustic neuromas were on the same side of the head, which was usually exposed to the phone. In the 2013 official report on the medical evidence for brain tumors, the International Agency for Research on Cancer concluded that radiation from cell phones is “possibly carcinogenic to humans”.