Three billion of us worldwide use them. One in five of us even sleeps next to one. And being parted from it has been compared to the stress involved in moving house or splitting with one's partner. What is it? The mobile phone. And our love affair with this technology suggests that far from considering it dangerous, we do not think of it as a health hazard at all. In fact we are more likely to get ill worrying that they don't work, or that our children don't have one. Anxiety over running out of battery life or credit, losing one's handset or not having network coverage affects 53 per cent of mobile-phone users in the UK, according to a study by pollsters YouGov.
Nevertheless, since their introduction, there have been concerns about the possible impact of mobile phones on health, particularly whether they cause brain cancers or increase the risk of Alzheimer's. So could they prove to be the hi-tech equivalent of cigarettes - seemingly harmless for decades, but in reality a health time-bomb waiting to go off? It's not just mobile phones that are being implicated.
The erection of phone masts on high buildings is often the trigger for local disputes. Not untypical was the row a few years ago in Wishaw, a village in the British Midlands. One of the residents, Eileen O'Connor, was convinced that the mast ushered in a variety of health complaints among local people, from nosebleeds to headaches. But for Eileen, it was much worse: at 38, with no history of the disease in her family, she contracted breast cancer.
Although there is no statistical evidence to support the claim of a cancer "cluster" in the village, Eileen firmly believes that the mast and her illness were linked and set up a local campaign group called SCRAM (Seriously Concerned Residents Against Masts). It is still going, and many other local groups have protested against masts in their communities. And what about an even newer innovation, the Wi-Fi networks which allow you to connect your computer directly to the internet without the need for wires? Some fear that these networks are yet another invisible source of harm.
The British Government, like many others, has, so far, dismissed such fears as exaggerated. The Mobile Telecommunications and Health Research (MTHR) programme, which is funded jointly by the UK Government and the industry, concluded that mobile phones, base stations and masts had not been found to be associated with any adverse health effects. The Health Protection Agency in the UK, which advises government on health issues and is state-funded, stated that as far as adults are concerned, Wi-Fi, phones and radio masts all operate on a power level well within the accepted guidelines.
Many cancer experts point out that mobile phones are not risk-free - but the risks they cause are most commonly associated with car accidents. But some people remain concerned. As recently as March, a study by an award-winning cancer expert said mobile phones, in particular, could kill far more people than smoking or asbestos. Dr Vini Khurana, an associate professor of neurosurgery at the Canberra Hospital in Australia, and fellow of the Royal Australasian College of Surgeons, suggested that people should avoid using them wherever possible and that governments and the mobile phone industry must take immediate steps to reduce exposure to their radiation.
Khurana's study was alarming. He suggested there was growing evidence that using handsets for 10 years or more could double the risk of brain cancer. Khurana reviewed more than 100 studies on the effects of mobile phones, and concluded "there is a significant and increasing body of evidence for a link between mobile phone usage and certain brain tumours". Khurana also called for a solid scientific study observing heavy mobile phone users for a period of at least 10 to15 years.
"It is anticipated that this danger has far broader public health ramifications than asbestos and smoking, and directly concerns all of us, particularly the younger generation, including very young children," he says in a research paper published on the website brain-surgery.us. He told the Larry King Show on CNN in May: "At this point in time, there's just over three billion users of cell phones worldwide. So that's half of our world population, or almost half.
"We've reached saturation points. For example, in Australia, there are 22 million cell phones and 21 million people. "And the concern is not just brain tumours, but other health effects associated or reported to be associated with cell phones, including behavioural disturbances, salivary gland tumours, male infertility and microwave sickness syndrome. "So we're not just talking about tumours, and I was not just implying brain tumours, but there are other health effects. And with so many users, and users starting at the age of three and up now, we should be concerned."
Asked if he used a mobile phone, he said: "I do. I mean they're invaluable, of course, as we all know. I use it on the speaker phone mode. I do not hold it to my ear." The French government recently warned against the use of mobile phones, especially by children who, it said, could be especially vulnerable to mobile phone emissions because of their thinner skulls and developing nervous system. Then the German environment ministry recommended that people keep their exposure to radiation as low as possible by replacing Wi-Fi with a cabled connection.
The city of Frankfurt decided not to install wireless systems in schools until there was more health research. Meanwhile, a group of 25 international scientists, known as the BioInitiative Working Group, carried out a major review of the evidence for the effect of microwaves on health. They found evidence for a raised risk of brain tumour from mobile phones, and also expressed concern about a possible raised risk of breast cancer, changes to genes, and inflammation in the blood vessels associated with conditions such as heart disease.
Some researchers have even called for mobile phones to carry health warnings, like cigarettes. But the case is certainly not proven. The Mobile Operators Association in the UK, for example, was dismissive of Khurana's study, describing it as "a selective discussion of scientific literature by one individual and presents no new research findings". Christine Jude, chief spokesman of the MOA, said: "The study reaches opposite conclusions to the World Health Organisation and more than 30 other independent expert scientific reviews that find no evidence of adverse health effects from low level radio signals.
"Certainly in the UK all mobile phones comply with the international health and safety exposure guidelines. And mobile phones automatically operate at the lowest power necessary to make a call." The American Cancer Society says people should keep an open mind, but it points out that the type of radio frequency that comes from a mobile phone is weak - halfway between an FM radio and the microwave. It also points to the fact that in Sweden, where mobile phones have been used the longest, brain cancer rates are flat.
Michael Clark, science spokesman for the Health Protection Agency, said: "There is still no hard evidence of a health effect, but it is early days. "This is new technology. We have recommended for nearly a decade a precautionary approach. We rely on expert groups to look at the scientific evidence and they have said that excessive use by children should be avoided. But we do realise that parents may want their children to have a phone in certain circumstances for perfectly good reasons.
"For adults, it's up to them. They could choose not to buy a mobile phone."