JACKSONVILLE, Fla. -

Tracey Neale is lucky she's the kind of person who checks her bank account regularly.

Several weeks ago, she noticed a $50 charge that wasn't hers, so she called her bank right away.

"And they asked me what my last charge was and I said I had gotten gas, and that was when they explained to me about gas skimmers. I didn't even know they existed," Neale said.

But they do, and the crime of skimming is on the rise.

"And obviously St. Johns County is not the only place that credit card skimming is occurring," said Sgt. Catherine Payne, of the St. Johns County Sheriff's Office. "It's throughout the state, throughout the nation."

Here's how it works: The thieves place a plastic covering over the credit card reader so customers don't know. It's there when they insert their card and pump their gas.

"So they leave thinking they paid for their purchase, they get their receipt, the skimmer itself collects from the magnetic strip on the credit card the account data," Payne said.

Channel 4 crime analyst Ken Jefferson says in many skimming cases, the person trying to rip you off is probably lurking.

"They'll stand on the outside as though they're just casually drinking a cup of coffee," he said. "Sometimes they're right next to you and you don't know it, pretending to pump gas or in their car doing something, but they're all around."

The good news, Jefferson says, is this is a fairly easy crime to thwart just by grabbing onto the card reader before you pump.

"You are the best enforcer there is because if you shake it or pull on it, if it's legitimate, it's not going to move. If it's a skimmer, it will move," he said.

"That's good advice," Neale said. "I mean, if that works, yeah, that's good advice. I'll use that."