The Smith County Sheriff's Office is investigating hundreds of cases regarding credit card skimmers at gas stations. It's happening across the state.

Sergeant Darrell Coslin with the Smith County Sheriff's Office said there is no pattern. He said it all comes down to the gas station to take preventative measures.

Tyler mechanic and gas station, Stewart's Donnybrook Automotive, was hit twice by skimmers. Owner Gary Stewart said his pumps are now criminal-proof.

He installed a lock that can't be recreated on each pump. At $25 per pump, he says it was an easy decision.

"It was one lock and one key. There were no duplicates available. You couldn't even make a duplicate," he said.

He said to look out for old, flat style key locks. Thieves can buy master locks, and hack in to pumps.

Card skimming happens in the blink of an eye, and it's virtually untraceable.

"The owner of the card does not see these fraudulent charge until they get their next bank statement, and then they realize they have an issue," said Sergeant Coslin.

He said the nature of the crime makes it difficult to catch the thieves, because the skimmers aren't on machines very long. Typically only a few hours, before anyone notices. Coslin said the time it takes for one to be installed is even shorter.

"The exterior skimmers. Just a second," he said. "They're only put on with double sided tape."

He said they're pretty easy to spot, and even easier to remove.

"If you just tug on it, and it comes off in your hand, you've found a skimmer," he said, talking about the card reader.

If the skimmer is internal, it's hard to tell.

Here's what you can do. First, pick a gas pump close with a clear view to the attendants. It will be less likely to be tampered.

Use a credit card. Coslin said it may take a while for the funds to be reimbursed into your account.

"We just have to try to catch them as quick as we can, find ways to prevent it from happening and move on to the next day," Stewart said.

If you want to make a complaint about a gas pump, or see one that looks like it's been tampered with, reach out to the Texas Department of Agriculture at 1-800-TELL-TDA.