While we are surrounded by radio waves emitted by the Cosmos, we have only known about them since the 1890s, when wireless transmission was first demonstrated.
However, It wasn't until the late 1980s, with the advent of the first mobile phones, that radio transmitters first started entering the home, and even then, it took until the early-to-mid 1990s before mobile phones became commonplace. The mid-1990s also saw the first consumer use of wireless networks, and just as with phones, only took a few years to become mass-market products.
Look around a modern home and you will see that we are now surrounded by devices which emit radio waves, from our mobile phones to laptops and tablets, wireless routers, baby monitors, cordless phones, wireless games console controllers, some TV and Hi-Fi remotes (although most use Infra Red), wireless burglar alarm systems, Bluetooth headsets, keyboards and mice, wireless weather stations and more.

More Information after the Break

Galaxy S3
Modern mobile phones have a peak transmission power of just 2W, although earlier analogue phones were as much as 3.6W
So does all this electromagnetic radiation pose any sort of health risk to us? This is a question that many scientists have been struggling to answer and it seems that trying to get a definitive answer is not easy.
There's no doubt that Radio Frequency (RF) energy can be powerful and dangerous. Microwaves ovens use radio waves to heat food, which is why they need proper shielding to be safe. High-powered radio transmitters, such as those used on military vehicles, have warnings to keep away from the antenna, because coming into contact with it while the radio is transmitting can give you a nasty burn (known as RF burn).
Microwave ovens use a frequency around 2,450MHz (2.45GHz), Bluetooth 2,400MHz to 2,408MHz, and Wireless LAN uses 2,412MHz to 2,484MHz. Other devices, such as baby monitors and burglar alarms tend to use FM frequencies (e.g. 433MHz).
Mobile phones vary from country to country and cover a wide spectrum of frequencies although the most popular are 850MHz, 900MHz, 1,800MHz and 1,900Mhz. While any radio wave with a frequency between 300Mhz and 300GHz is classed as a microwave, it doesn't mean that they all have the same characteristics.

How bad are microwaves?

Microwave ovens are able to heat food for three reasons; the waves are highly focused, the metal box of the oven prevents the waves from dispersing, therefore they are fully absorbed by whatever is in the oven and thirdly, the emission power is very high (up to 1,000w). In contrast, a Bluetooth headset, wireless land or mobile phone's RF emissions are unfocused and unconstrained, while the emission power is much lower.
Bluetooth devices range from 1mW to 100mW, Wireless LANs between 32mW and 200mW, while 3G mobile phones have a maximum power output of 2 Watts, but will typically be operating at around 500mW, although the first analogue phones had a peak output of 3.6W.
Microwave
Microwave ovens use focussed wave, at very high power and trapped within a metal container, to heat food
From this it's fairly obvious that the amount of RF energy emitted by most devices, is incredibly low. However, any device which operates near the same frequencies as a microwave oven, i.e. around the 2GHz mark, could potentially generate some of the same effects, including localised heating of tissue. It is this heating effect which has led some to believe that microwave frequency radio waves are detrimental to health.

What about phones?

In 2011 the International Agency for Research on Cancer (IARC) classified mobile phones as possibly carcinogenic, although the World Health Organisation has said that "to date, no adverse health effects have been established as being caused by mobile phone use". A number of studies have been carried out, but as mobile phone use has only been widespread for around 15 years or so, so far, there has no direct evidence of a link between mobile phone use and cancer.
One of the largest studies was carried out in Denmark and involved around 420,000 people, who had been using mobile phones for 21 years (1982 to 1995). Despite the fact that the users would have been using the higher powered analogue phones, as well as lower-powered digital phones, the researchers concluded that there was no evidence for an association between tumour risk and mobile phone use, even in long-term users.
Bluetooth
Bluetooth headsets are very low power devices and enable you to keep your mobile away from your head
So what about other health risks? There have been many stories which claim that RF exposure can interfere with sleep patterns. Research here is contradictory, with one Finnish study showing no ill effects, others have found that pulsed RF can have an effect on the brain. Some people even believe that being soaked in radio waves has other effects upon the body, such as fatigue, lack of concentration, headaches or memory issues, and this is known as Electromagnetic Hypersensitivity.
However, in 2010, a review of 46 studies into electromagnetic sensitivity found that there was no robust evidence for the existence of electromagnetic hypersensitivity. In double-blind tests, those who claim to suffer from hypersensitivity were unable to conclusively determine whether a RF emitting device is on or off.

Reducing exposure

While RF emission power levels are regulated by national legislation, some manufacturers, it seems, take extra steps to reduce your exposure. It has been discovered that in Apple's latest iPad, there is apparently a proximity sensor, which will reduce the power of the device's 3G radio, when it detects a solid object (such as any part of your body) within 10mm top of the screen. However, according to Pong Research, it's not just human tissue which triggers the sensor, most iPad cases do as well.
Ipad mini
The iPad contains a proximity sensor, which can be activated by many standard cases and which reduces the 3G signal strength
Pong does have a vested interest in these claims, however, as it markets a range of cases which it claims not only stop the proximity sensor of the iPad activating, when fitted with a case, but which also direct the RF energy of your mobile device away from your head., using a passive, coupled antenna. Unfortunately these are claims we can't verify, as we simply don't have access to the necessary testing equipment, however, Wired has an extensive writeup on Pong's claims and comes to the conclusion that yes, these cases do in fact live up to their claims, when tested in a compliance testing lab.
One of the points Pong makes is that most SAR (Specific Absorption Rate – a measure of how much RF energy is absorbed by the human body) tests are done on models of adults heads. The argument is that a child's head, especially one under the age of 10, has a much thinner skull than an adult and the brain is more vulnerable to the effects of RF radiation.
This is a fair point and while some more recent tests have been conducted using head models based on MRI scans of a child's head, most studies have been based on adults. Studies that have used models of a child's head have shown increased absorption of microwave frequency radio waves.
Pong
Pong's cases are custom made for each phone model, so that the case's antenna is in the optimal position
So, the question is, should you be worried about the emissions your wireless devices are giving off? This is the billion-dollar question and to our minds, still hasn't been answered. So far the evidence would suggest that adult users are at very low risk, but more research needs to be done. For children, the risks would certainly appear to be higher. Trying to police your child's phone use is probably impossible, so reducing exposure seems like the next best option.
Using a Bluetooth headset is certainly one way to reduce the amount of RF radiation your head is exposed to from your phone, although they are not the easiest things to use and far too easy to misplace. Using a case that directs radiation away from the head would seem to be the next best option and Pong's cases would certainly seem to fit the bill.