Officers are urging people to be "on their guard" following reports of distraction burglaries and people making unsolicited approaches to elderly residents.
They said they have recorded offences in Castleford, South Heindley, Pontefract, Wakefield and South Elmsall in which men have either cold called and then overcharged people for gardening work, or pretended to be tradesmen and then burgled properties.
Inspector Helen Brear of Wakefield Neighbourhoods West: “We are aware of several reports of males targeting elderly and vulnerable residents and offering to carry out odd jobs for them or using this excuse to gain entry to burgle their homes.
“We believe some of these offences are not necessarily linked but there has been a clear pattern of offending targeting people who are vulnerable in our communities.
“On occasions were work has actually been carried out this work has either not been necessary or grossly overpriced, very much amounting to fraud.”
Recent offences include a burglary in South Elsmall on January 9 in which three men attended a house and told the elderly woman they had been sent to check double glazing. While there, they broke in and searched a bedroom.
In another incident on January 16, two men knocked on the door of an elderly resident on Wakefield’s Peacock Estate and asked if she needed odd jobs doing.
The victim declined but agreed to give one of the men a glass of water. They stole her handbag and other property when she wasn't looking.
Detective Inspector Dan Tillett of Wakefield CID, said: said: “I would always remind residents that they are under no obligation whatsoever to agree to accept services provided by someone who cold calls at their property and should not let a person into their home if they have any doubts about them.
“A number of enquiries are ongoing into these recent incidents and we would ask residents who have elderly relatives who they think may be vulnerable to these kind of frauds to check on them."
Anyone with information about bogus workmen is asked to contact CID by calling 101. Information can also be given to Crimestoppers anonymously on 0800 555 111.