How to catch a cheating partner

Love rats, run for cover - your day of reckoning is at hand. Valentine's Day yesterday was the perfect occasion for the UK launch of a lie-detector phone line that will tell you if the passion's gone from your relationship and you bore your partner rigid. And it's not the only method of romantic surveillance: now we can all be private detectives. Type the words "catch cheating spouse" into Google and over 14,000 entries come up from companies in the serious business of breaking up relationships. From kits testing stains of dubious origin to software that will record every keystroke made on your loved one's computer, the market is teeming with ways and means of checking up on cheats.

The "Love Detector" exploits voice analysis technology used by police and fraud agencies to help you discover what your partner's voice is telling you that their words aren't. At £1.50 a minute it's not cheap, but use it now to confirm your doubts and it could save you the cost of dinner (although divorce lawyers are even more expensive). It has already gone down a storm in Israel, where it receives 1.5 million minutes' worth of calls a month.

Simply call the love detector number (09064 070 000), then call your lover while the Love Detector listens in. After the conversation is over, stay on the line while it gives its professional analysis. Unfortunately it doesn't exactly tell you "this man is a lying pig" or "she's sleeping with your brother", but it rates things like how interested they were in what you were saying, and how much hesitation and passion there was in their voice.

According to Ido Pollack, one of the men responsible for bringing the line to Britain, it is just a bit of fun. "The technology behind it works and it's useful but I wouldn't make a marital decision based on it. It's really for new and potential couples, something to use to see if a certain colleague in the office likes you."

Another snooping device comes from the US company CheckMate, which sells a kit for £49.99 that will detect traces of semen left behind after sex. Nice. All you have to do is rummage around in the laundry bin for a dirty sheet or pants and take a swab of an offending stain, pop it into a special solution, and hey presto you can "instantly prove infidelity and show there are grounds for divorce". One woman on the website seems ecstatic: "I ordered your kit and found semen...now I can make his life hell."

Another business, TruTest, offers a similar kit for about £60 but with the added bonus of UV light to help you find stains invisible to the naked eye. "You can be your own private detective," it promises.

And if fishing around in the laundry basket and applying chemicals to your lover's briefs isn't really your thing, there is an array of technology at your disposal. A company called OverSpy will let you monitor everything that your partner does on their computer by sending you e-mail reports of the websites they've visited and e-mails they've sent. "Is your spouse cheating?" they ask. "Don't you have the right to know?" Well, when they put it like that...

And the new generation of mobile phones lets you track your partner's every move from the comfort of your own home. T-Mobile's new SDA phone comes with CoPilot satellite navigation system that allows you to track the movement of the phone by logging on to a website and entering a password. Used by companies to monitor their staff, it can easily be used by controlling or suspicious partners. A spokesperson said: "We don't really shout about it but this is the perfect device to check if your partner is cheating on you, Ralph Fiennes style..."

Another UK company, Pipistrel, has produced software that allows you to retrieve deleted text messages from your partner's phone - if you can just get your hands on their SIM card. Again, the manufacturer says that the product wasn't designed for this purpose but knows the software could be used this way, although it doesn't condone it. But at just over £60, it doesn't break the bank of any suspicious spouse or paranoid partner.

If you want to tap into your boyfriend's answerphone, it's not a problem. Want to open your girlfriend's letters without her knowing? There's a manual to show you how... but who really uses these things? According to the Garden Pharmacy in Covent Garden, most of their CheckMate kits are sold to men.

So are these products the modern equivalent of the chastity belt, another way for men to keep their women on leads? According to the feminist author of Love, a User's Guide, Jane Knowles: "When men they say they care for a woman, they really mean they control her.

"It's true that working women now have many more opportunities to meet other men and this, combined with the shift in power created by women earning more money, can make men feel vulnerable and paranoid. They also love gadgets and there is an element of them wanting to be the good guy playing the detective."

Not according to the American manufacturer and self-proclaimed "creator of the infidelity testing industry", Brad Holmes, who argues that just as many women buy as men - and he is empowering them.

"Men are dogs!" he argues, "There are women who don't even own a car, they're stuck at home all day and he comes back with semen stains in the back of his underwear! Women have got a right to know!"

But is it right to snoop on your partner, even if you are suspicious of them? Not according to the psychotherapist and relationship expert Gladeana McMahon. "To go to these lengths you either know that something is wrong or you're completely paranoid," she says. "If it's the former you should be talking to your partner, and if it's the latter you'd better be careful that you're not the one dumped for being a nutter."

Relate counsellor Denise Knowles argues that these products can be dangerous and "exploit the paranoia of vulnerable people".

Not their problem, according to Brad, who says: "Guns are dangerous but it's not the manufacturer's fault if a crazy person buys one. It's amazing what people will do to each other."

He's right, of course. It is amazing what people can do, and infidelity has been around for ever, but what's even more amazing is the business to be made out of it. And as long as there's money in it, the love detectives are here to stay. It's enough to make you stay single.

Love Detectives

Claire Rimmer, 22, from Birmingham, caught her boyfriend cheating by tracking him via his mobile phone

Just like all the clichés I started to suspect something was up when my boyfriend of six months became distant and started working late. He also didn't answer the phone when I rang him, and he always had his mobile switched off when we were together. I wanted to check it for text messages but he was really protective of it. I must admit I tried to hack into his e-mail but I couldn't figure out the password. I know I should have talked to him about it but I couldn't face the showdown and guilt if he denied it. My techie friend told me that I should follow him using the new T-Mobile phones with satellite navigation systems that let you log on to a website and track the movement of the phone.

So for a Christmas present I bought him one. He was gadget mad and loved it, and I assuaged my guilt by thinking that even if I found out nothing, at least he'd still like the present. I got the opportunity to use it a couple of weeks later when he said he was going to the gym, having already been earlier that day. I logged on to the site and watched on the map as he pulled out of our road, drove past the gym and to his ex-girlfriend's house. By the time he got home his bags were packed. He didn't have a clue what was happening when I told him to leave, and that I knew he was cheating on me. He didn't deny it.

I don't feel ashamed of what I did, but I would have felt very guilty if he was innocent. If you have an inkling it's better to know. If I'd have asked him straight out, I know he would have lied to me. I didn't tell him how I'd done it but all my girlfriends knew and were very impressed.

Hannah Reed, 26, from London, thinks that the Love Detector line saved her relationship

I tend to get a bit insecure in relationships and started to feel that my boyfriend wasn't as into me as I was him. For the first six months it had been pretty casual, but around Christmas I wanted to find out whether he thought we had a future. He is one of those people who doesn't express his emotions, and I was reading that as him not having any feelings for me. So I called him on the Love Detector and tried not to be sound too suspicious as I asked him if he thought things were going well and if he was happy with our relationship. He said that he was happy and he loved me, but from his tone I wasn't at all convinced. When he hung up though, the Love Detector said that his passion levels for me were really high (nine out of 10) and that he was being sincere. It might sound stupid but that one computer telling me that my relationship was good really put my mind at rest. After that, I think I relaxed and backed off a bit, which then made him a lot more demonstrative. Things are really good and yesterday, on Valentine's Day, we moved in together. I didn't tell him what I'd done, but he'll find out now! I'm sure he won't mind - all's well that ends well.