Brat Nav... the GPS that can tag your teenager (or errant husband) absolutely anywhere in Britain

A device the size of a large matchbox is being launched that exactly pinpoints a carrier's location through a global positioning system accessed by computer or mobile phone.

The gadget, called buddi, can be clipped to children's clothing or carried in their pockets. Parents then log on to see their child's position on a detailed map via satellite tracking.

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Would you track your husband and children with this sat nav? Join the debate at Reader Comments below

Buddi also has two buttons that can be pressed if the wearer is lost or in trouble to alert friends or relatives through an emergency call centre active 24 hours a day.

It is the first such device to be launched in Britain and is the brainchild of Sara Murray, 38, a former marketing consultant. She spent two years developing the idea as a result of her own experiences as mother of a daughter, now 14.

"When my daughter was little she got lost in a supermarket and in that moment of panic when I realised she was missing, I wished I had something I could put on her to keep track of her," she said.

"I found her safe and sound but, as she grew up, there were many more occasions when I worried where she was and thought there must be a better way of monitoring her. Then, two years ago, I came up with the idea for buddi."

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Ms Murray, who lives in Pimlico, South-West London, said her idea could help other vulnerable people such as those with dementia or learning difficulties.

"We live in difficult times and any service that can provide people with the confidence that they can be traced within seconds, or alert people in emergencies, is something I am sure will help people," she added.

The device is backed by organisations responsible for vulnerable people, such as Parents and Children Together and the National Autistic Society. It goes on sale on the internet next month, costing £299 to buy plus £20 a month to operate.

But critics warn it could encourage parents' paranoia and lead to children being over-reliant on the system rather than developing skills to cope with potential dangers. Michele Elliot, director of children's charity Kidscape, said: "Tracking devices could be useful in certain circumstances, such as for children with learning disabilities or elderly people with dementia.

"But I would warn parents to use their common sense and not become too dependent on them.

"I worry that giving these devices to children will send out the message that the world is very dangerous and they can't ever be out of contact with their parents. They might never learn important lessons for themselves."

Ms Murray has also launched a product called petbuddi, which can be attached to a pet's collar and used to track them.

But the version for children has a more intriguing alternative use. Maybe it is just the job for suspicious wives fretting about a husband "working late" again.