Customers have reported £300 swiped from their accounts after using a cash machine outside a bank.
Police are investigating two reports of cards being swallowed since November 1 at the cash machine at Barclays Bank in Stonecot Hill.
Police have seized a device which was taped to the underside of the top of the machine and above the keypad.
They are urging customers to take a close look at cash machines before inserting their bank cards.
Outside of banking hours customers need to be most vigilant.
If customers believe a cash machine has been tampered with in some way the police say do not use it and to tell the bank or Sutton Police station on 101.
If you see anyone acting suspiciously near a cash machine, dial 999 immediately.