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Hands-Free Kit Concerns Remain
Our latest tests confirm that hands-free kits can indeed increase the radiation from mobile phones. Following the tests in this controversial area, our conclusion and message to consumers remains: don't rely on a hands-free kit to reduce the amount of radiation emitted from a mobile phone.
Previous Which? tests
However, although both the Which? and DTI tests were measuring the strength of the electric field from the phones and hands-free kits at the head, the DTI was using a different type of test called a specific absorption rate (SAR) test. We think the way these tests are carried out on hands-free kits is flawed and means they can't pick up the effect our tests uncovered.
As the DTI published its report, we were midway through our latest round of testing. We wanted to see whether we would find the same results as in April if we used more phones and kits in different combinations.
The Latest Which? Tests
The critical factor
SAR test limitations
There is another important difference between ERA's tests and SAR tests. ERA measured the radiation from the kits and phones at the same place - inside the head at ear level. With SAR tests, the probe moves around inside the test head and the equipment picks out the area where the reading is highest. With the kits, this was again at the ear. But with the phones, it was at the jaw and cheek. So, unlike our ERA tests, SAR tests don't automatically give a reading for radiation emissions from phones at the ear.
We think the standard that SAR tests phones have to go through should be extended to include this so that kits and phones can be compared properly. We also think more research is needed to investigate whether there are differences in the effects of RF radiation emitted at the ear (close to the brain) and at the cheek and jaw.
How we carried out our specially-designed tests
We used a probe inside a dummy head to measure radiofrequency radiation emissions. First we measured the emissions with just the phone handset next to the ear. Then we measured them with the hands-free kit earpiece in the ear and the phone at about waist level. From this position, the scientists moved the phone up and down so that they varied the distance between the tip of the phone's aerial and the earpiece (distance 'd'). They took readings for thousands of different positions.
We found that this distance 'd' determines how much RF radiation the earpiece emits. The maximum emissions occurred when 'd' was between 40cm and 47cm, and again between 58cm and 75cm, depending on the kit being tested. Between 47cm and 58cm the emissions fell again so that they were lower than the levels from the phones. In the positions where the kits were giving higher readings, they were between 46 per cent and 259 per cent higher than the readings from the phones. In the positions where they were cutting emissions, the scale of the change was less marked - anything from 8 per cent to 97 per cent.
Exploring SAR tests
We have found two possible explanations for this. First, the design of the SAR test rig doesn't replicate how someone would normally use a hands-free kit. Most importantly, the wire couldn't hang down straight - as it did when we took the highest readings in our other tests. Second, we found that the SAR test system looks for the point in the head where there is the highest level of radiation - and gives a final reading for only this area. But we found that kits and phones emit the highest levels of radiation in different places: kits emit most at the ear; phones emit most at the user's jaw and cheek.
The health question
Despite these partial reassurances, radiation levels remain a concern to the users of the 34 million mobile phones in the UK. Hands-free kits were originally thought to reduce radiation - but our tests show that, while they can cut levels, they can also increase them. This depends on the phone, the kit, your height and where you position the phone. Unfortunately, there's no way that an individual can work out the best position for them to minimise the effect.
We want the government to take our findings into account and devise a new standard for testing hands-free kits. But remember: if you're concerned, the most important safety-first advice is to keep the number and duration of calls to a minimum, whether you use a phone with or without a hands-free kit.