According to research from insurer Norwich Union, and Tracker, a tracking and vehicles recovery company, the number of incidents where cars have been stolen using car keys taken from the home have doubled in the last two years.
Tracker said that it had recovered more than £7m worth of cars taken with stolen keys last year - a 52% increase from 2000.
Insurers are now warning homeowners to be careful where they put their car keys and to view the security of their keys as they would other household items, particularly in the light of a recent increase in "car-jackings".
Expensive mistake
The 'hook and cane' approach, where a hook and cane is used to reach people's keys though their home letterboxes, is one method that is being used by thieves to obtain car keys.
Norwich Union said that its claims investigators in the north west of England have reported a massive increase in the use of this technique.
It estimated that between 30 and 40% of motor theft claims in the area now involve this approach.
"Many people just throw their car keys down when they get home and give little thought about what that could mean if they were burgled," said Jill Willis of Norwich Union.
"Most of us would never dream of leaving £14,000 lying around the home - the average cost of a new car - so it pays to be more cautious."
Take care with keys
Three in five people surveyed admitted that they don't worry as much about their security of their car keys as they do about other household possessions.
Norwich Union is recommending that motorists take greater care with their keys and recommend people should keep them in a locked cabinet or hidden away - not lying on the hall table.
But it said that there "no plans" to start refusing insurance claims if people did not take care of where they stored their keys in the home.