On ATM's, they can look like they're designed to blend in. And if they go unnoticed when a person swipes a bank card, that skimmer swipes the information from the magnetic strip.
Cory Mathes is a security officer for the State Employees' Credit Union, he says in the last two weeks, some 300 members have had money stolen.
"We started getting a lot of calls saying, my card was used in such and such city, I'm here in Raleigh," Mathes said.
But thieves aren't targeting SECU members, officials say skimmers appear to be in gas pumps scattered around the Triangle.
"On the whole, they do seem to be certain gas stations," Mathes said.
Unlike ATM's where the skimmer will almost always be on the outside with the gas pump, you may never know you're being skimmed.
It's because there are universal keys that open the pump, allowing a thief to hide a device inside the machine. But to use your credit card, thieves don't just need the strip, they need the pin number - somewhere they'll have placed a camera recording the keypad so when you enter your number, shielding it with your other hand may be the key to keeping your information safe.
And police say that's the important thing, vigilance.
Authorities say six men have been spotted in surveillance pictures trying to get money out of an ATM with stolen information.
They say if you recognize any of the men call Raleigh police.