Burglars have walked into nine unlocked homes in Corby in the past two weeks.
Now police are appealing to homeowners to make it more difficult for the thieves by making sure their doors and windows are secure.
Inspector Carl Sturman said: “Unfortunately, too many people still leave doors unlocked – often they simply forget to check or think someone else in the house must have done it.
“In the past two weeks, more than a third of all house burglaries have happened because the property was left insecure.
“Burglars are opportunistic and if they come across a door or even a window that’s been left unlocked, it’s an easy target for them.
“Properties where the front door opens straight onto the street or back onto an alleyway can be particularly vulnerable, but I would urge everyone, wherever they live, to please make sure they’ve locked up properly, both when they’re in the house and when they go out.
“Even if someone is at home, if a front door is open, it can take just seconds for a burglar to steal a handbag or set of keys left in the hall.
“We’ve also had a number of shed and garage break-ins and I would encourage people to check that all outbuildings are secured with good locks and alarmed if possible.”