A high-tech system is being tested in London to help families of dementia sufferers trace their loved-ones if they happen to wander off.
More than 600,000 people in the UK suffer some form of dementia
Sufferers have been given a mobile phone with a global positioning system (GPS) installed.
If they get lost, carers or relatives can pinpoint their location with an accuracy of up to five metres.
Imperial College London and Hammersmith Hospitals NHS Trust are working with Ealing council on the technology trial.
The New Technologies in Elderly Care (NTEC) scheme is open to residents of the borough who are over 60 and suffer from dementia.
"This is a novel approach to giving patients their independence while ensuring that families and carers are able to maintain a watchful eye," said lead researcher Dr Frank Miskelly.
"This and other NTEC projects will enable the elderly to live longer at home, and at the same time reduce the burden on health and social care systems."
The researchers hope the system could soon be used around the UK.
Residents carry the mobile phone with its GPS receiver, when they leave the house.
If a carer or relative needs to know of their whereabouts they can call the control centre, manned round the clock at the council's offices.
By getting the co-ordinates from the phone, they can pinpoint the person's location, up to within five metres, enabling help to be quickly sent out.
Dr Miskelly and colleagues have also been testing the use of electronic tagging, similar to that used on offenders, to monitor dementia patients.
However that system limited them to the confines of their home and garden, setting off an alarm if they left a small area covered by a central monitor.
There are more than 600,000 people in the UK who suffer some form of dementia, with the numbers growing as more people are living longer.