For many, chastity belts conjure up images of medieval knights storming in from battle, unlocking their women and plunging into passion.

Now, hundreds of years after they first became popular, the belts are back. But today's "knight" is more likely a nine-to-fiver, and the person being unlocked is more often than not ... a man.

"Most of the belts we sell are male belts," said Matt Montierth, sales assistant at California-based chastity belt vendor m.b. productions. Their slogan? "We hold the key to your fantasies."

Unlike in medieval times, when chastity belts were used to prevent women from cheating and/or being raped while their husbands were away, today's devices are used largely for fun — to enhance the fondness that absence can inspire, if you will.

"Someone locks their partner before going to work for the day, calling them every once in a while to keep things heightened. It's a play thing," Montierth said.

While m.b.'s belts — which come in metal and leather combinations and cost between $88 and $133 — are not the chastity belts pictured in encyclopedias, such belts do exist.

Britain's Tollyboy specializes in "traditional" love-locks, or stainless steel belts that can be hidden under most clothing and worn for long periods of time.

"I have a customer who only takes his off two times a year — his wife's birthday and Christmas," said Tollyboy owner Richard Davies. His belts go for about $350 for the female version and $500 for the male model.

So who would spend this kind of money to be sexually frustrated?

"I have customers who are businessmen, airline pilots, doctors, accountants," said Davies, who added that up to 85 percent of his customers are males who have "high-pressure, high-powered lifestyles."

And it seems the traditional function of chastity belts — enforced fidelity — is making a comeback.

Mike, a 46-year-old Tollyboy client and printer, was "mostly" happily married for more than 20 years when he had an affair "which led to all sorts of trouble," he said.  He credits the chastity belt with saving his marriage.

"I wear my belt 24/7, my wife having both keys," Mike continued. "I find it hard sometimes to stay locked up, but someone else being in charge of when I can be let out has increased my sexual drive, and also made me look at how I treat my wife."

Davies said he has been contacted by several couples in similar situations.

Kitty Christensen, president of Chicago's Paul C. Leather, also said she often makes belts for people who are traveling (i.e. vulnerable to infidelity).

"We just make 'em and people do what they want," Christensen said.

But Alexandra Myles, a Massachusetts-based couples and sex therapist who has worked with clients who have used the belts, was less amused by the chastity-belt renaissance.

"As part and parcel of S&M play they can heighten the level of frustration and excitement," Myles said. "But it's not a healthy way to ensure fidelity in a couple. As a matter of fact, it's a pretty sick way."