Scientists believe that small errors, such as forgetting to take a teabag out of a cup or not putting milk back in the fridge, could point to the deadly disease.
The US study suggests families should be aware that if a loved one begins making mistakes at home they may be at a higher risk of developing dementia in the future.
Researchers at Temple University, Philadelphia, observed 100 people, including 50 with dementia, asking them to carry out everyday tasks.
The jobs included making a breakfast of jam on toast with a cup of coffee, packing a lunch for a child and wrapping a present.
Dr Tania Giovannetti, co-author of the study, said: “Early on, we can look at very subtle errors called micro-errors.
“When we compare healthy agers to young people, there are more micro-errors in healthy older adults than young adults and they’re associated with memory problems and cognitive changes.
Healthy agers reach out to objects inefficiently, they touch them when they don’t need to, they make all these extra little actions. “We think that might be the beginning of a problem. If you have more of those, then you are more vulnerable to decline in future.
“It’s really too early on to say if there’s a problem but those subtle little signs might be something to keep an eye on.”
Dr Giovannetti and her team identified two different types of task-processing failures which could help diagnose which type of dementia people have and lead to more effective care.
They found people with Alzheimer’s disease tended to miss out vital steps or forget that they needed to complete a task.
Those with other forms of dementia tended to have problems putting the steps in the right order.
Dr Giovannetti added: “Early on, the problems can be very subtle.”
The team now plans to use the findings to help families identify potential dementia risks. The study is published in the Journal of Neuropsychology.