Stamford police are warning bank customers to be vigilant when using ATMs after a recent uptick in scams.

They say it's been years since they've seen this scam tactic, but it has resurfaced.

The skimming device is meant to try to read the magnetic strip on debit cards, and cameras are strategically placed to catch a customer putting in their PIN.

Ever since chips and touchless scanning were added to cards along with the magnetic strip, the scam has decreased.

"Any time you have the opportunity to use your chip on your card it's going to increase your security of your password, your private information," said investigator Sean Coughlin.

But in recent weeks, police have recovered two devices in Stamford, another in Greenwich and one in Bridgeport.

All were found at bank ATMs.

Police want people to be cautious and alert when using ATMs. They recommend covering the pad with your hand as you punch in your PIN.

"If you can use any way to kind of shield your hand from entering that pin, that's huge. If you notice the machine itself is off, feels strange putting the card in if it doesn't insert, if doesn't read properly, if you get some sort of error, there might something wrong, just try a different ATM," said Coughlin.

Police say if you think the ATM you're using may be affected, contact the bank and they will work with police to investigate.