NEW figures show a third of burglaries in Kirklees are by sneak-in thieves.
Police figures reveal a staggering rise in the number of sneak-in burglaries in Huddersfield and Dewsbury in just four years.
Kirklees community safety officer, Ms Maroof Shah, described the figures as "extremely worrying" and urged people to change their habits.
She said: "This is an opportunistic crime and the thieves rely on people leaving open their windows and doors - particularly in the warm weather."
Her message was supported by police crime prevention officers in Huddersfield and Dewsbury.
Det Chief Insp Colin Prime of Huddersfield Police said his figures showed that the problem had doubled over the last four years in Huddersfield.
Four years ago sneak-in burglaries accounted for 14% of all burglaries in the Huddersfield division. That figure rose to 16.5% two years ago but has now increased to 30%.
He said: "Sneak-in burglaries are a major problem which can so easily be tackled.
"We really are talking about getting back to basics.
"Don't leave handbags and keys near a door and don't leave doors and windows open."
Crime Prevention Officer Pc Colin Whiteley of Dewsbury Police said his figures showed that sneak-in burglaries accounted for 4.9% of all burglaries four years ago, 19% of burglaries last year and 30.7% of all burglaries at the moment.
Of the 2,097 burglaries reported in Dewsbury, 644 were sneak-ins.