Bank users are being warned about suspicious devices at ATMs after a man was charged over a card-skimming scam linked to unauthorised transactions totalling more than $100,000.

Key points: The 32-year-old Estonian man, in Australia on a working visa, has been refused bail

The 32-year-old Estonian man, in Australia on a working visa, has been refused bail Police say two ATMs were fitted with thin magnetic strips that record card data

Police say two ATMs were fitted with thin magnetic strips that record card data "Several items" allegedly used in the scam were found in the man's car

WA Police said two ATM machines in Perth's northern suburbs were fitted with the devices designed to illegally scan and store card information, allowing criminals to make the unauthorised transactions.

The transactions occurred between August 31 and September 28 this year.

A 32-year-old Estonian man in Australia on a working visa has been charged with four offences, including conspiracy to commit an indictable offence and possession of stolen or unlawfully obtained property.

Police said "several items of interest" used in the card-skimming scam were found in the man's car when he was arrested in the southern suburb of Kardinya.

Card skimming involves a magnetic strip being inserted into the card slot of an ATM. ( Supplied: WA Police )

They also said initial investigations indicate the offences "may be linked to an overseas established criminal network".

"We will be sharing all the information we have gathered with our Commonwealth and international intelligence and law enforcement partners to assist with the further investigation into those potential overseas links," police said in a statement.

The man was refused bail when he appeared in Perth Magistrates Court and will reappear at the end of the month.

Card skimming devices hard to spot

Card skimming uses a magnetic strip which is inserted into the card slot of an ATM to read and store data when an individual makes a bank transaction.

The data is then extracted onto a USB.

Detective Sergeant Ian Lewis said ATM users needed to be aware of the discreet devices, even though they were difficult to detect externally.

Police say "several items of interest" used in the ATM scam were found in the man's car. ( Supplied: WA Police )

He urged people to be alert and cautious.

"Take into account some basic procedures you can do to protect your personal information and keep that secure," he said.

"You can do that by simple steps, by covering your hand when entering the PIN on the ATM.

"There are still things on the exterior of the ATM to look for … [such as] a camera device which is stuck on to the exterior of the ATM.

"So that would be the obvious link for people to look for, particularly over the keypad."

ATM users have been urged to contact their bank or police if they suspect any suspicious activity.