Skimming devices have been found three times on an ATM machine in Bolsover in recent weeks.
The incidents were reported at the Post Office on Cotton Street and users’ bank cards have not been returned by the machine.
Officers are appealing for information about suspicious behaviour and are asking people to call 101.
The Bolsover Safer Neighbourhood Policing Team have also posted pictures of the ATM on their Twitter account with and without the device, and asking people to see if they can spot the difference, in a bid to help raise awareness of the locally.
PCSO Ben Perry said: “Please be vigilant when you use a cash machine, and take a look around the machine to see if you can spot anything unusual before you use it.
“Always cover the keypad as you enter your PIN number and if you insert your card and it appears to be stuck or is retained then check the facia and contact your bank or card issuer immediately.
“If you notice anyone acting suspiciously then please contact the police as soon as possible.”