Martha returns home from a three-day business trip to find a cigarette butt in an ashtray under the bed. It's not her brand. Martha's husband, who doesn't smoke cigarettes, tries to convince her the stale butt is hers. She doesn't believe him.

Suspecting the worst, Martha takes the smoking gun to a private lab for a DNA analysis. After comparing the DNA fragments from the cigarette filter to Martha's own saliva sample, the technicians conclude that the tell-tale cigarette was smoked by a woman -- and it definitely wasn't her.

Whatever happened to the lipstick stain on the collar? In the old days of freewheeling adultery, a hang-up call in the middle of the night was the worst a philandering rogue had to worry about. Now there are itemized cell-phone bills, call-display screens, automobile tracking devices, Internet history folders, stealth-mode keystroke-recording software programs and spray-on sperm detectors all waiting to trip you up. Every advance in technology increases the odds of getting caught. And there's a whole lot of cheating going on: Figures from a Stanford University survey reveal that 25 to 40 per cent of married women and 50 to 60 per cent of married men have had at least one promiscuous liaison.

Since 1999 a Seattle-based company has been selling semen-detection kits over the Internet (http://www.getcheckmate.com/). This $49.95 (U.S.) test detects  an enzyme found in high levels in male ejaculate. The test detects traces of semen on items of clothing, and might be used, for example, by a woman who suspects that her husband has just returned home from the arms of another woman.

"A lot of people laughed at us at first," says Brad Holmes, Marketing Director. "But now, they're just amazed. We've begun a nationwide advertising campaign. And we expect to sell at least 1,000 units a month. Most people, at one time or another, think their spouse is cheating. Whether or not it's true, this is a good way to find out."

More and more, however, betrayed lovers are trying to answer questions about infidelity for themselves. And sometimes, all it takes is a phone call. The cellular phone has become one of the major causes of marital breakup in Britain, according to the British counseling service Relate.

"Growing numbers of couples are coming "for therapy sessions," having discovered that an affair was being conducted via a mobile," a spokesperson for the company told The Observer last year. Citing the case of one TV producer who was dumped after he inadvertently hit the redial button on his phone and left his partner a message meant for his actress lover, explaining that she was "far more sexy" than his partner, the spokesperson added: "We are seeing more and more relationships hit in this way."

Others have been tripped up by call display, saved messages, last-call return and received call logs. You can even buy a call-display monitor to plug into a hidden jack so your partner is unaware that you have the gadget. But the most dangerous modern convenience of all? Itemized billing, a common feature on cell phones in Canada, lists the phone number of every call dialed and received. The introduction of itemized billing in France, where the extramarital affair is practically tied with soccer as the nation's favorite sport, caused a huge uproar as thousands of affairs were uncovered. France Telecom eventually backed down and replaced the last four numbers on the bill with asterisks.

Rakes everywhere will agree that modern technology is ruining their lifestyle. "The computer age is killing us," A.J. Benza recently wrote in a Playboy magazine article titled The Perils of Adultery. "There was a time when beepers, car phones, faxes and voice mail were the perfect ways to keep in touch with your girlfriend. Not any more. Get rid of them all.

"Beepers, and the numbers they display, leave a wonderful paper trail for your wife to follow. A car phone is especially horrible the first time you forget to turn it off and it rings when your wife is with you . . . .

"And whatever you do, don't mess up your home phone with caller ID or any of that other mumbo-jumbo. All it adds up to is your wife's first big collar. She'll feel like Nancy Drew for the rest of her life when you say you're calling from work and the number flashing on the caller ID box is definitely not your work number."

Ha. They ain't seen nothing yet. Last summer, a telecommunications company in Hong Kong unveiled technology that could potentially turn cellular phones into tracking devices that will allow cell-phone firms to pinpoint a caller's location to within five meters. Although the technology is intended to locate 911 callers in distress, some observers say it's only a matter of time before location-tracking information becomes available to the masses, somewhat like TravelEyes. Available over the Internet for approximately $500, this GPS mapping software program can be hidden in a car, then downloaded onto a remote computer, to reveal the exact route the car has taken and the length of each stop.

Do-It-Yourself Sleuthing is taking its toll on private detectives. Ken Willett, an investigator with the Toronto agency Tattle Tales, says his old-fashioned gum-shoe business is slowing down. "People want to try to catch their partners on their own." Willett also sells pin-hole cameras, voice-activated micro-cassette recorders that plug into hidden jacks and other high-tech spy gadgets. And he's doing a roaring business, which makes up for the lack of surveillance requests.

Although modern technology might be responsible for tripping up the modern adulterer, it has provided new opportunities for cheaters. Anthony DeLorenzo, a private eye in New Jersey who operates an infidelity support Web site (http://www.infidelity.com/; see sidebar), says the Internet is "the best thing" that ever happened to private investigators.

"My business has increased 15 to 20 per cent because of housewives who are having affairs on the Internet." In the past, he says, the majority of his clients were women who wanted their husbands trailed. But now, the ratio has flipped.

Willett has witnessed the same revolution.

Take Mark, as a case-in-point. The 30-something business consultant was happily married to Angela, a stunning blonde event planner, for four years. Two years ago, he began to suspect that she might be fooling around when her best friend launched into a lusty affair. Mark went to Willett, who told him to save his money; in Willett's previous experience, jealous husbands were almost always wrong. Willett sold Mark a phone-recording device. But when that didn't turn up anything, Mark went back and begged Willett to take his money. 'Does she use the Internet?' Willett asked.

"That's when it hit me," recalls Mark. "She was on it every night and I had no idea what she was doing." A friend in the IT department at work made Mark a program that would send all of the e-mails his wife sent and received to his e-mail account. Nothing strange there. Then he made a second program which recorded all of her chat-room conversations. Bingo.

"There were 140 pages," Mark recalls. 'I sat down with a latte and started to read. It was brutal. I realized she and her boyfriend had met once or twice for coffee and dinner, but the, you know, key meeting was still being planned."

Mark hired Willett to trail his wife and her Internet lover to their romantic weekend getaway in Niagara Falls. Willett's men managed to get pictures of the two kissing, a room-service bill, plus credit-card receipts from the hotel. Mark's wife tried to explain it all away as a one-night stand until he confronted her with the saved computer cache. They were divorced shortly thereafter and Mark has since remarried.

"I've met the perfect woman," says Mark. "She doesn't know anything about computers."

VIRTUAL SUPPORT FOR THE BROKEN-HEARTED

You are not alone any more.

Infidelity.com is the brainchild of Anthony De Lorenzo, a New Jersey private investigator, author of 28 Tell-Tale Signs of a Cheating Spouse and darling of the daytime talk-show circuit. Billing itself as the No. 1 infidelity support network, the Web site has received 500,000 hits since it went up in October. This popular rendezvous for the broken-hearted offers a directory of experts (from divorce lawyers to fitness coaches), support groups, professional advice chat sessions and a bubbling discussion board on which the wronged partners can console one another and plot their revenge.

Herewith, a sample of the chat-room conversation:

TOPIC: Need inexpensive 'spy' equipment -- please read
Author: wondering

Posted: 05-08-2000 01:50 a.m.

I've been away for awhile, things have somewhat calmed down a bit in my life . . . . but I am still so paranoid about my boyfriend possibly cheating. It is starting to affect other areas of my life. (i.e. -- work, family, friends) I am getting desperate and although I don't want to spend a ton of money, I was wondering if any of you know if there is any way of tracking incoming/outgoing phone calls -- besides caller i.d. We have visible redial -- but it only shows the last number called, which could easily be erased. I need a piece of equipment that is tiny, and that he would not notice. Please, if any of you can help, I'd really appreciated.

I remain forever,

Wondering.

Author: angbri77

Posted 05-08-2000 06:49 p.m.

Hi . . . . Well I would probably tell you that if your 'gut' is telling you he's cheating then he probably is!!! But, there is a product out now called Checkmate and it is a semen detection kit . . . . It's like $50.00 for two kits or something like that and you can use it on ANY fabric or bedding . . . So, I hope you get the truth that you are looking for . . . Good luck!

Author: stronglady

Posted: 05-11-2000 07:55 p.m.

Call the phone company. A girlfriend of mine did to check on her cheating spouse, and she got a report that was FREE! Also, they would know of other devices if this service isn't offered in your area.

Another possibility is to get a different phone that had a better call history on it. I have one that the 'dial log' stores a bunch of numbers, and I have caller ID for incoming calls.