A brainwave test could detect the early signs of Alzheimer's in just three minutes - years before typical diagnosis.
In a trial of the simple test, developed at the University of Bath, the technology identified specific memory issues in people with mild cognitive impairment (MCI), an early risk factor for dementia.
The simple test could therefore help to identify those most at risk of the disease and most likely to benefit from new Alzheimer's drugs.
The test, called Fastball, involves showing patients rapid images and recording the brain's automatic response. It uses EEG, a technology that records the activity of the brain using small sensors on the scalp.
Dr George Stothart, a cognitive neuroscientist in the Department of Psychology at the University of Bath, who led the study said: "We're missing the first 10 to 20 years of Alzheimer's with current diagnostic tools.
"Fastball offers a way to change that - detecting memory decline far earlier and more objectively, using a quick and passive test."
The Alzheimer's Society estimates there are around 982,000 people with dementia in the UK, but more than a third do not have a diagnosis. The number is expected to rise to 1.4 million by 2040.
Dr Stothart added: "There's an urgent need for accurate, practical tools to diagnose Alzheimer's at scale. Fastball is cheap, portable and works in real-world settings."
The study included 52 patients with mild cognitive impairment (MCI) and 54 healthy older adults. MCI is a decline in memory or thinking skills that can be an early sign and risk factor for Alzheimer's.
Patients on the trial also completed a number of neuropsychological assessments of memory, sustained attention and general cognitive function, as well as the Fastball test.
Researchers found those with amnestic MCI - when the main symptom is significant memory loss, such as forgetting appointments and recent conversations - showed significantly reduced responses to the Fastball test compared to healthy patients and those with non-amnestic MCI.
Researchers re-tested the group after one year and found Fastball "showed moderate to good test-retest reliability" in healthy older adults.
The study also demonstrated for the first time that the test can be performed in the home of patients.
Chris Williams, chief executive of BRACE Dementia Research, which supported the study, said: "Fastball is an incredible tool that could offer anyone who, for whatever reason, cannot access a dementia diagnosis in a clinical setting."
Reacting to the findings, Sir John Hardy, professor of neuroscience and group leader at the UK Dementia Research Institute at UCL, said: "Identifying individuals early for cognitive decline is going to be of increasing importance as therapies for Alzheimer's and other dementias are developed and this protocol Fastball seems as if it may be helpful in this regard.
"What it does not do, and does not claim to do, is distinguish early Alzheimer's from other causes of decline and this latter is also important.
"Because of this, it is likely that additional tests, biomarker or imaging, would also be needed for this second important aim."
Dr Julia Dudley, head of research at Alzheimer's Research UK, described the results as 'encouraging'. She noted: "This study, in a small group of people, suggests that it can be used to measure mild memory impairment, which for some people can be an early sign of diseases like Alzheimer's.
"However, as participants were only followed up one year later, we don't know if those people will definitely go on to develop dementia.
"Longer-term studies in larger, diverse groups of people are needed to find out if this technology can predict how memory problems will unfold over time."