Take a close look at your local ATM machine before withdrawing money, say Bedford police after handing two separate cases of bank fraud in recent weeks.

In both instances, thieves placed an almost-undetectable overlay over the ATM machines at the Chase Bank branches in Bedford Village and Katonah and left them there for a few hours. Customers made withdrawals and had their account information stolen and personal identification numbers recorded—and weren't even aware of it until they checked their statements later.

A skimming device was placed on the ATM in Katonah on Feb. 6 around 11:30 a.m. and reported to the police on Feb. 24; in Bedford Village it was placed on Mar. 17 around 6:45 p.m and reported to police on Mar. 25. In both cases, the skimmer was left for a few hours before thieves came back to remove it—and in both cases, video surveillance revealed the suspects. 

"We don't know right away because the customer doesn't know right away," said Detective Sergeant Tom Diebold. "It takes time to identify the problem and to go through the security tapes to see when it happened."

The suspects appeared different in each video but were unrecognizable in puffy coats, hats and sunglasses, he said.

After removing the skimmer, which swiped information from the slot where customers insert their debit or credit card, and a camera, which recorded people typing in their PIN numbers, thieves took the information to banks in Brooklyn to withdraw larger sums of money.

"I would urge bank customers to notice your surroundings—sometimes the thieves will stay in the area after putting a skimmer on, to make sure people are using it," said Deibold.

He also recommended covering your hand as you type your PIN number so it can't be filmed from above."This is not a new problem, but it seems to have picked up in the region." 

Mike Fusco, a Chase Bank spokesperson, said that he could not comment on the frequency of these types of thefts, but he did confirm that the bank has reimbursed all customers who lost money through the scam. 

"We encourage customers to routinely check their bank statements and to notify the bank immediately of any losses so that they are not liable for the fraud," he said.

Click here to see some photos of ATM skimmers on Snopes.com.