Editors' note: This is the third of a three-part series on issues related to cell phone radiation. Revisit Tuesday's story on the inconclusive state of research on cell phone radiation, and Thursday's story about the trouble with federal safety standards, or click here for a roundup of related coverage.

When my sister--a mother of four--was shopping for a new cell phone last summer, she wanted to know: what's the safest cell phone in terms of radiation

At first, I simply directed her to CNET's Quick Guide: Cell phone radiation levels, which shows the specific absorption rate, or SAR level, for some of the most popular cell phones on the market. SAR is the rate at which your whole body absorbs energy from a radio-frequency (RF) magnetic field. Every model of cell phone sold in the U.S. is tested and certified by the Federal Communications Commission to ensure it has a SAR value less than 1.6 watts per kilogram.

The FCC has established a protocol for testing cell phones, and after each model is tested it's assigned an SAR value. This value, which must be below 1.6 watts per kilogram over a mass weighing 1 gram, is supposed to represent the maximum amount of radiation that this phone can produce under the most stringent conditions.

But as I started working on this CNET special report on cell phone radiation, I realized that the FCC's SAR limit is not enough to help concerned consumers limit exposure. As I mentioned last week in the second installment of this special report, "The trouble with the cell phone radiation standard," the studies on which these limits are based are outdated. Also, cell phone radiation levels vary depending on the strength of the wireless signal the phones are receiving. And the amount of radiation to which you could be exposed is dependent on how close the phone is to your body. Even holding the phone a few centimeters from your head can greatly reduce the amount of radiation you could be exposing yourself to.

To help readers figure out their best options for reducing exposure to cell phone radiation and to answer other questions related to protecting oneself, CNET has put together this FAQ.

What's the real meaning of the World Health Organization's recent report that cell phones may cause cancer Last week, a division of the WHO classified cell phones as a "possible carcinogen." This means that though no definite link has been established between cell phone use and some forms of cancer, there's enough evidence that the group believes more research is needed. Other "possible carcinogens," according to the WHO, include lead, exhaust from gasoline engines, chloroform, and coffee.

Previously, the WHO had said there was not enough evidence to even suggest a link between cell phone use and cancer. So the recent news is a departure from the previous stance. And it may spur governments and other groups to change their recommendations for cell phone use and safety. So far, neither the Federal Food and Drug Administration nor the FCC here in the U.S. have changed their recommendations.

You mentioned the SAR values assigned by the FCC. Should I be looking for a phone with a lower SAR if I'm concerned about reducing my exposure to cell phone radiation The FCC has said on its Web site that consumers shouldn't use the SAR value to compare the "safety" of cell phones. It maintains that all phones sold in the U.S. must test below the 1.6 watts per kilogram limit, and that therefore all phones that have made it to market are safe.

And because the amount of radiation a phone emits can change, the FCC SAR value is not really that meaningful. Still, some experts say that looking at the SAR value of a phone is a good starting place for consumers concerned about cell phone radiation exposure.

"There's no harm in disclosing the SAR value," said Henry Lai, a researcher at the University of Washington, who has published several studies and has peer-reviewed several more studies on the effects of electromagnetic radiation. "It may not be particularly meaningful, but the point is that it gives people a choice, and it gets them thinking about other ways they can reduce their exposure."

So should I avoid using a cell phone I'm sure there are some people who might advocate that you should not use a cell phone at all. But in today's world, that's not really practical. And it's probably unnecessary, especially when there are ways you can reduce exposure. For example, automobile accidents kill more people every year than many diseases do, but nobody has suggested that people stop driving their cars. Instead, the government requires safety standards, like air bags, and drivers take safety precautions, such as wearing seat belts. Consumers can also take precautions to minimize the risk associated with cell phones.

"We would never tell people to stop using their cell phones," said Gil Friedlander, co-founder and CEO of Tawkon, which makes a smartphone app that monitors cell phone radiation exposure and alerts people when the exposure is likely high. "But when you drive a car, you put on your safety belt. When you are trying to get to a healthy weight to prevent illnesses like heart disease, you count calories."

What precautions can I take to reduce exposure to cell phone radiation

&149' 'Don't put your cell phone right next to your body. Moving a cell phone even an inch from the body can greatly reduce radiation exposure. Signal strength falls off as the square of the distance to the source. This means that if you double the distance to the source, which is the cell phone to your head, the signal strength would be four times less, since two squared is four. If you triple the distance, the signal strength would be nine times less, and so on. At 10 times the distance between the cell phone and your head, the signal strength is 100 times less, and at 100 times the distance, it would be 10,000 times less.

&149' 'Keep conversations short. The less you talk on your cell phone, the less exposure to radiation you will have. So by keeping voice conversations short, you're limiting your exposure.

&149' 'Use a headset. Experts recommend using either a wired headset or a Bluetooth headset. While you may still be exposed to some radiation using either type of headset, it's still a lot less than holding the phone to your ear. If you do use a Bluetooth headset, I'd recommend taking it out of your ear when you're not using it. There's no need to continue to expose yourself to low levels of electromagnetic radiation when you don't need to, since we still don't know the long-term effects of radiation exposure at these low levels.

&149' 'Use the speaker phone function of the cell phone. For the same reason you'd use a headset, using a speaker phone is another good option. It keeps the cell phone away from your body, and you don't have to worry about using a headset. Of course, the downside is that everyone around you will hear your conversation, so this may only be something you do when you're at home or somewhere private.

&149' 'Turn your cell phone off when you are not using it. For example, turn off your phone when you go to sleep at night. Or at the very least turn off the cellular radio in your phone. Many smartphones, such as the iPhone, allow you to put your phone in "airplane mode." This shuts down the cellular radio portion of your phone. You can also turn off the Wi-Fi radio, too, just to be safe.

&149' 'Avoid using your cell phone in places where you get a poor signal. Many consumers also don't realize that cell phones emit different amounts of radiation depending on where they are with respect to a wireless operator's cell phone tower. Cell phones are constantly communicating with cell phone towers, but the further away the subscriber is from the cell tower, the weaker the signal. In order to connect to the cell tower, the device must boost its power, which increases the amount of radiation emitted. This means that if you get poor reception in your basement, you should move upstairs to your living room, where you have better reception, to talk on your cell phone. Tawkon's Friedlander noted that a minute of talk time in a "red zone," where the radiation is likely higher because of a poor cell phone signal, is equivalent to the amount of exposure you'd get talking on the phone for three hours in a "green zone," where reception is good and the radiation emitted from a cell phone is much less.

&149' 'Text, IM, or use the Net more than talking on your phone. When you're texting or using your phone to access the Internet, you aren't holding it up to your head the same way you would if you were talking on it. So texting and using other forms of communication that don't require you to put the phone to your head or right next to your body are good ways to reduce exposure.

&149' 'Carry your cell phone in your purse or backpack instead of in your pocket. Again, it's all about creating distance between you and your cell phone. So if you carry your phone away from your body, then you are reducing your exposure.

I've heard device makers warn that cell phones shouldn't be held too close to your head. Is this true User manuals from most cell phones suggest keeping the phone a certain distance from your head rather than pressed up against your ear. The iPhone 4 manual says: "When using iPhone near your body for voice calls or for wireless data transmission over a cellular network, keep iPhone at least 15 mm (5/8 inch) away from the body, and only use carrying cases, belt clips, or holders that do not have metal parts and that maintain at least 15 mm (5/8 inch) separation between iPhone and the body."

Many people have interpreted this as a warning from Apple about keeping the device a certain distance from your body. But the disclosure is written that way because that is how the cell phones are actually tested.

In the testing procedures the FCC uses to certify that cell phones don't exceed the 1.6 watts per kilogram SAR limit, the commission chose to test the phones at a distance of between 0.59 inches and 0.98 inches (1.5cm to 2.5cm) from the body. It also tests the devices in a "body-worn" configuration and specifies that this should be done with the device in a belt clip or holster. If a belt clip or holster was not supplied with the phone, the FCC has told testers to assume a separation distance of between 0.59 inches and 0.98 inches (1.5 cm to 2.5 cm) during a test.

In other words, the FCC's testing protocol does not test for phones that are broadcasting at full power while inside your pants pocket or pushed up against your ear, two of the most likely ways cell phones are actually used.

Given the current testing guidelines, it's hard to say whether cell phones sold in the U.S. would exceed 1.6 watts per kilogram if they were in a pocket or against your ear. But officials at the FCC have said that there is enough of a cushion built in to the current standard that they believe that all cell phones in the U.S. are safe.

Tawkon radiation alert.

I've seen advertisements for cell phone radiation shields that supposedly block cell phones from emitting radiation. Do these shields work The Federal Trade Commission, the nation's consumer protection agency, says that manufacturer claims regarding so-called "shields" are mostly baseless.

According to the FTC, there is no scientific proof that these "shields" significantly reduce RF radiation exposure from cell phones. The agency warns that some of the shield products that claim to block radiation from the earpiece or another part of the phone can interfere with the phone's voice signal, which may cause the device to use even more power to communicate with cell phone towers. And this could lead to the cell phone emitting even more radiation.

What about the app from Tawkon that was mentioned earlier in this article Is that app useful in reducing radiation exposure The Tawkon app supposedly monitors the SAR level and alerts users when it gets above a certain limit. To be honest, I don't know how accurate the Tawkon application is. There are a lot of factors that go into calculating the SAR level of a phone at any given moment. But the company claims its application uses an algorithm that measures your SAR by using the phone's GPS technology and accelerometers to gauge the position and proximity of the device to the body to determine the amount of radiation that's being absorbed by the person using the phone.

The company is also using anonymous information culled from its users to provide free access to a radiation map, powered by Google Maps, that makes radiation exposure levels publicly available to users worldwide.

The app also provides an in-home or office map that lets users predict where radiation would be the lowest and highest, based on their individual usage. The idea is that given this information, consumers can choose to use their mobile phones in areas where radiation is the lowest, or they can reduce exposure in areas with more radiation by using a headset. The app also provides personal statistics based on usage that give wireless subscribers an indication of how much radiation they've likely been exposed to during the last call, day, week, month, or six months.

So assuming that the way it measures SAR is accurate, the Tawkon application could provide you with more information about when and where your phone is likely to emit more radiation, and then it allows you to decide how you will change your behavior to minimize exposure.

Tawkon initially released its app for Research In Motion's BlackBerry operating system. And now it offers the app for the Google Android OS. The company submitted its app to the iPhone App Store, but it was rejected. However, iPhone customers can still use the app if they jailbreak their phone and get the app through Cydia, a software application for iOS devices that lets a user find and download software for jailbroken iPhones, iPod Touches, and iPads.

Because the application must be tested and calibrated for each individual piece of hardware, it is not yet available for every BlackBerry or Android device. So potential users should check Tawkon's Web site for device availability.

The app can either be purchased from the BlackBerry App World or Android Market for $9.99, or users can get the app for free if they agree to accept mobile advertisements. The iPhone app for jailbroken devices is free and does not include advertisements.

Are children at an increased risk for cell phone radiation exposure and its effects Many experts believe that if risks exist owing to cell phone radiation, children will likely be affected more than adults. There are a couple of reasons for this. For one, children today are likely to begin using cell phones at a much younger age than their parents did, which means they will be exposed to this low-power radiation for a much longer period of time over their lifespan than today's adults.

And secondly, children have smaller heads and thinner skulls than adults. And as a result, radiation is believed to penetrate more deeply into children than adults. What's more, cell phones may have a greater effect on children's brains because their brains are still developing.

Some researchers have suggested that children might be more likely to suffer from memory loss, sleeping disorders, and headaches as a result of cell phone radiation exposure, as well as be at increased risk of some cancers later in life. Several countries, including Russia, Germany, France, Israel, Finland, and the United Kingdom, have issued warnings against children using cell phones.

In the U.S., meanwhile, efforts to require warning labels or requirements to provide more information about the SAR of a particular phone at the point of sale have so far been largely unsuccessful. Check out CNET Reviews editor Kent German's recent story that surveys the current state of cell phone radiation warning legislation.