If you’ve ever enjoyed a garlicky meal, you may have followed it with a quick breath check by cupping your hands to your face and huffing. At times like this, a personal stink sensor could come in handy.

With that in mind, a Japanese company has unveiled a prototype cell phone with a built-in bad-breath meter that will let you know if you need to reach for a mint. It also keeps track of your activity level, your pulse, and your paunch, thanks to a built-in pedometer, a pulse meter, and a body-fat analyzer, which sends a small electrical signal through your body to assess its composition.

The prototype Wellness Navigator–a slider phone with a touch screen, manufactured by Mitsubishi–was shown off last week at the Ceatec 2007 exhibition in Tokyo by Japan’s NTT DoCoMo, one of the world’s leading mobile providers.

Besides alerting users to their racing pulses and foul breath, the phone enables them to set exercise goals and share health data with friends and family. They can also track their caloric intake, using their typical daily diets to establish a baseline and adjusting for splurges by clicking pictures of pizza or spaghetti. Once customized, the phone offers users perky personalized messages encouraging them to keep exercising or get a good night’s sleep.

NTT DoCoMo won’t discuss its plans to market the phone or give any indication of how much it might sell for, but spokeswoman Makiko Furuta says that the target market is flabby middle-aged businessmen and diet-conscious young women.

The Wellness Navigator is the latest in a parade of Japanese cell-phone innovations, many of which have been slow to find a U.S. market. NTT DoCoMo customers can already pay for train rides, movie tickets, and groceries with a wave of their phones, and a phone that doubles as an alcohol breathalyzer has been popular with bus and taxi companies.

Pedometers and pulse meters have been available in small gadgets–wristwatches, for instance–for some time. But it’s the new phone’s “halitosis meter” that’s piqued the most interest among tech enthusiasts and health experts alike.

Bad breath is a complex bouquet of gases, mostly sulfides, which a spouse–or a very good friend–can subjectively evaluate with a sniff. Objective assessment is harder. Gas chromatographs can provide detailed information about the chemical composition of an exhalation, but they’re expensive and require trained operators. Sulfide monitors are used in many clinics, but they require regular recalibration, and they can’t detect some of the stinky gases implicated in bad breath.

The Wellness Navigator incorporates a sensor that detects sulfides and ranks the user’s breath on a scale of 1 to 10. However, “this notion that this little cell phone could do the work of this very elaborate equipment is just highly unlikely,” says Pat Lenton, a research fellow at the Oral Health Clinical Research Center at the University of Minnesota.

“I’d have to see it to believe it,” says Christine Wu, a professor in the Department of Periodontics at the University of Illinois at Chicago, who is on the board of the International Society for Breath Odor Research.

“Is it a gimmick?” says Glenn Clark, a professor at the University of Southern California’s School of Dentistry. “Probably. Is it a good idea? Well, it wouldn’t hurt.”

Bad breath is often caused by bacteria hunkered down on the back of the tongue, but it can also betray problems elsewhere in the body, such as gastrointestinal maladies, liver disease, and diabetes. Anybody who gets a bad-breath bulletin from the Wellness Navigator needs to “follow up and find out what’s causing it rather than just buying a bunch of mouthwash,” adds Beatrice Gandara, a lecturer at the University of Washington’s School of Dentistry.

“I love it that phone companies are getting into the health game,” says Ray Browning, a research instructor at the Center for Human Nutrition at the University of Colorado. He cautions, though, that the “phone’s downside really centers on its accuracy.”

Even if the Wellness Navigator doesn’t offer entirely accurate assessments of bad breath or body fat, health experts say that it could still help people track their progress toward health goals.

“Don’t focus on the number,” Browning says, “but what you’re ideally trying to do is change some of these numbers.”

Research also suggests that immediate personalized feedback and encouragement like that doled out by the Wellness Navigator can help people achieve health and fitness goals.

“Prompting is critically important, especially in terms of changing health-related behaviors,” says John Jakicic, chair of the Department of Health and Physical Activity at the University of Pittsburgh, who has studied the use of cell-phone text messages and wearable monitoring devices in weight-loss programs. “The more immediate you can make it, the better,” he says. “I get that feedback, I know where I am.”

“The more specific messages are to their target,” Jakicic adds, “the more effective they are.”