BERKLEY, Mass. -- Value cards from grocery stores and pharmacy chains are now a common sight on people's key chains. But these little items designed to save you money could be making you vulnerable to criminals.

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Watch Susan Wornick's Report

NewsCenter 5's Consumer Reporter Susan Wornick reports that some customers using the automatic money-saving cards have opened themselves up to theft. After finding someone's lost keys Pam Leite of Berkley saw the Stop and Shop loyalty card and called them, hoping they'd contact the owner. She was stunned at the clerk's response.

She asked for the numbers on the bottom of the SKU. I gave them to her, and within seconds she gave me all the information.

Within seconds, Stop and Shop happily offered the name, address and telephone number of the stranger whose house and car keys Leite had found.

"I could have gone into their home or taken their car in the middle of the night," Leite said. "I was like, this is scary that I could get that information that easy."

Eleanor Antonelli of Berkley is the woman whose lost keys Leite found. She is, of course, thrilled that they were returned by an honest person, but she is also livid that Stop and Shop released her identity, including her unlisted telephone number, so easily to someone who could have had criminal intent.

"Suppose they had done something to my little dogs … and we would have never known who did it, because Stop and Shop gave out our number.

Officials for Quincy-based Stop and Shop refused to talk on camera, but in a written statement, they apologized, saying they are "committed to customer privacy," and while associates are trained not to give out personal information, in this case "the policy was not adhered to." The policy was "immediately reissued and reviewed with all appropriate personnel."

But that's not enough for Antonelli, who has now removed all the loyalty cards from her keys.

"Because I figured if Stop and Shop did it, Shaws will do it. Ames will do it. Any of the other stores will do it," she said.

We decided to check other stores and discovered that's not the case. After calling several of the major chains that offer loyalty cards, we found that only one shared personal information.

Blockbuster quickly gave us a customer's name address and telephone number after we read them the tag number. When we questioned Blockbuster, a PR person told us "our policy is not to do that. Our personnel made a mistake … and we're definitely going to look into it."

Loyalty cards have become quite popular and convenient when they're on your keys, but Buyer Beware.

"I've told I don't know how many people, 'Take all your tags off,'" Antonelli said. "I said if you keep them on, you're crazy, because you don't know what's going to happen."

Stop and Shop stands by its key tag program, claiming that since its inception, it has actually returned 11,000 sets of keys. But remember, if you carry around personal information on your key ring, there's always a chance that it can fall into the wrong hands.