A male has been in the Wheatley area trying car doors with a view to theft, according to South Yorkshire Police.
He was last seen on Town Moor Avenue at about 5am yesterday, and previously in Wheatley Hills at the same time.
Police officers ask you to please check your cars for valuables and make sure they are locked, adding: "Also keep your keys upstairs when you go to bed.
"There has been a number of theft from motor vehicles in the last few days, probably due to the heat and windows being left open, so please be vigilant. (This goes for house windows as well)."