Farmers are being urged to be on their guard following a suspicious incident near the village of Shottle.
The Derbyshire Police warning comes after a man visited a farm in the area and offered to sell tools including chain-saws on June 25.
He was later reported to police who put out a warning.
Community Information officer, Tim Parkin, said: “If you are tempted to buy items in such a manner check for postcode marks and other signs the items may be stolen.”
Anybody who witnesses a suspicious incident should phone police on 101.