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DENVER -- The 7-Eleven store at East 17th Avenue and Pearl Street in Denver looks like most other convenience stores.

There are gas pumps, the signature 7-Eleven Slurpee on the door and an ATM inside.

However, looks can be deceiving. Ben Carlson knew something about the ATM just wasn't right.

"It felt like it was glued on there," he said.

Carlson said he typically pulls and tugs at card readers to make sure there's not a skimmer hidden nearby. However, this is the first time he yanked one off the machine.

"It felt like all my paranoia was warranted finally," he said. "It was tough to get off. Everybody in the store thought I was nuts because I was tearing an ATM machine apart."

Police across Denver metro area say they're seeing more card skimmers, not just on ATMs, but also at gas pumps.

"It is happening, and not just here, but all across the country," said Jenny Fulton, a spokeswoman with the Jefferson County Sheriff's Office.

Fraud detectives say there are several things that can be done to minimize the risk of becoming a victim of identity theft because of a card skimmer.

Their best advice is to always pay for gas indoors.

However, if paying at the pump, they strongly recommend not using a debit card. A thief could not only steal credit card information, but also the bank account number.

Also, always look for fraud-tampering labels on credit card panels at the pump. If the tape is torn, a criminal has likely opened it and another pump should be used.

Last, authorities recommend choosing gas pumps closest to the front doors of the building.

"The criminals who are using (the skimmers) are going to use the outer pumps, typically," Fulton said.

Skimming devices are becoming smaller and more sophisticated. Criminals don't even have to physically retrieve them.

They can download personal information using Bluetooth from a half block away.

Some gas stations are also becoming more sophisticated in the ways they try to protect customers from identity theft.

King Soopers and City Market stores have new alarm systems that immediately shut down a pump if it's tampered with.

As for Carlson, he'll continue to closely inspect ATMs, always worried a thief could be trying to steal his personal information.