Baby monitors, bought by parents to keep their children safe, may instead be harming them, some scientists fear. They warn that the devices are bathing the infants in radiation at an age when they are most vulnerable to it.

The radiation, similar to that given off by modern cordless phones, is part of the increasing electronic smog to which mobile phones, their masts and Wi-Fi systems also contribute. The monitors use the same digitally enhanced cordless telecommunication (Dect) technology as cordless phones.

Over recent weeks The Independent on Sunday has exclusively reported growing concern that the smog may be damaging human health. The paper reported that Sir William Stewart, chairman of the Health Protection Agency, has been privately pressing an investigation into the effects on children of installing Wi-Fi networks in schools.

Baby monitors are typically placed close to infants, who are particularly at risk from radiation. An inquiry by Sir William into mobile phones seven years ago reported that a one-year-old child could absorb about twice as much per kilogram of body weight as an adult.

Babies are especially vulnerable because their bodies and nervous systems are still developing and because they will have more time to accumulate exposure to the radiation and for any delayed effects to develop.

Professor Denis Henshaw of the University of Bristol said the monitors are "being marketed without any checks and balances or even studies into their effects".

Professor Olle Johansson of Sweden's Karolinska Institute said that the cells of a growing baby are "very susceptible". Powerwatch, an information service on radiation, says: "A Dect monitor placed in your baby's bedroom will expose them to more pulsing microwave radiation than living near to a mobile phone mast would do. We have had a number of reports from parents that their babies did not sleep well and cried a lot when they used Dect monitors." It added that older wired and analogue monitors do not raise the same concerns.

Dr Roger Coghill, who runs a laboratory specialising in the radiation, suggested that the Dect monitors should be placed at least 10 feet from infants. He said, "You want to hear what a baby is up to, but you don't want to harm him or her."

A spokesman for one company which sells the monitors said it did not believe that there was any danger from the monitors, which more than meet international safety standards.