Police are warning elderly residents to be on their guard for a team of burglars claiming to be council staff.
A police spokesman said there had been 14 burglaries and other attempted incidents in Northampton since Thursday.
Officers are urging people not to open the door to unexpected callers and to make sure the elderly are warned.
Safety Officer Kate Wright said: "We need people to call us if they see any people behaving suspiciously."
People of all ages
While the caller keeps the householder occupied, an accomplice sneaks in and looks for cash.
Community Safety Officer Kate Wright said: "We need people to call us if they see any people or vehicles behaving suspiciously in their area and we need them to call us straight away.
"This team or teams of offenders are obviously going from house to house, street to street to look for people to target and everyone should be alert to the fact that they are operating in the county now."
She said people of all ages - not just the elderly - should be on the alert for bogus callers.
She urged anyone with information about the incidents to ring the police or to contact Crimestoppers anonymously.