Bryan takes a polygraph.

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In Gary's research, he found that 93 percent of husbands would not voluntarily tell their wives if they'd had an affair. What's a wife to do? Gary suggests suspicious wives should ask their husbands to take a lie detector test—also called a polygraph.

When searching for a company to give the test, Gary suggests you consult the American Polygraph Association. "Make sure the person is licensed, insured and a member of that organization," he says. "Even though they're not admissible in court, they're 95 to 98 percent accurate. There are a lot of court prosecutors who will make a decision whether to prosecute or not based on a polygraph test, even though it's not used for court. They are much more sound than people tend to think."

Last summer, Jennifer discovered e-mails from another woman to her husband, Bryan, which she considered inappropriate and evidence that the woman was pursuing him. After an argument, Bryan agreed to end his communication with the woman.

But in January, Jennifer got a phone call from a man she assumed was the other woman's husband. And she learned Bryan had met up with the other woman while he was on business in Florida—where he and the woman both grew up. Bryan denies ever having any sexual contact with the other woman, but Jennifer remains skeptical. "In my head I'm thinking, 'You've lied to me every step of the way,'" she says. "'Why wouldn't you lie about this piece of it?'"

Bryan agreed to take a lie detector test.