Residents are being warned after a skimming device was found on a ATM in Milton, Cambridgeshire.
Customers became suspicious after a machine at Tesco made some strange noises, and they were unable to withdraw cash.
The remains of a skimming device were seized on July 24.
A man and woman using a silver Skoda Octavia were spotted acting suspiciously in the area.
Crime Reduction Officer Rachel Carr said: "If you are not happy with the ATM and feel it may have been tampered with, go inside the store or building and ask staff to contact police. We would prefer to come and investigate, than to miss the opportunity and someone is defrauded as a result.
"Look out for anything that seems out of place: if there are scratches, or if the card holder is loose. Devices are placed on machines for a short time, and if you move, or tap it, it's likely to come off."
People who are concerned they may have been affected by card skimming should check their bank statements and report any unusual activity.