It could be a dieter’s best friend or worst nightmare: technology that knows how much a person has just eaten, knows how many calories he has burned off, offers suggestions for improving resolve and success, and never lets him cheat. And it’s all done by a small, stick-on monitor no bigger than a large Band-Aid.

The calorie monitor, which is being developed by biotech incubator PhiloMetron, uses a combination of sensors, electrodes, and accelerometers that–together with a unique algorithm–measure the number of calories eaten, the number of calories burned, and the net gain or loss over a 24-hour period. The patch sends this data via a Bluetooth wireless connection to a dieter’s cell phone, where an application tracks the totals and provides support. “You missed your goal for today, but you can make it up tomorrow by taking a 15-minute walk or having a salad for dinner,” it might suggest.

Caloric-intake monitoring has long been the bugaboo of dieting systems. There are devices, such as the bodybugg, that can measure energy expenditure through a combination of accelerometers, pedometers, and temperature and sweat sensors. But the intake side is much trickier to track. Currently, the most reliable way to determine caloric intake is meticulous diary keeping or having a trained professional do the calorie counting.

“What they’re working on here, I would argue, is the holy grail in health and wellness,” says Don Jones, vice president of business development for health and life sciences at Qualcomm, which specializes in wireless technologies. Other than the two methods mentioned above, he notes, which aren’t scalable and aren’t always accurate, “there are no good methods for calculating caloric intake.”

PhiloMetron won’t yet reveal exactly what makes its patch tick, but the company says that it consists of a single chip surrounded by numerous sensors, electrodes, and accelerometers, embedded in a foam adhesive patch. The system, which is designed to be replaced once a week, measures a variety of things (temperature, heart rate, respiratory rate, skin conductivity, possibly even the amount of fluid in the body), then throws the data into an algorithm to calculate the number of calories consumed, the number burned, and the net yield. Caloric-intake measurements are accurate only to about 500 calories–about two Snickers candy bars. But PhiloMetron CEO Darrel Drinan says that it is much more accurate in determining net gain or loss and is most useful for measuring trends over the course of a week or a month. In fact, the system only provides users with rolling 24-hour totals and no instantaneous data.

An increasing number of studies conclude that a diet’s success or failure depends on simply decreasing the number of calories consumed. Be it a Mediterranean, Atkins, Weight Watchers, or South Beach diet, it’s the caloric bottom line that matters.

“A repeatable trend is a more useful value than an accurate number,” says Drinan. “The trend line helps you establish the pattern to your behavior.” He says that the company is working with the largest device manufacturers, weight management, and pharmaceutical companies–“and none believe we need more sensitivity because of the long-term nature of the underlying problem.”

PhiloMetron’s prior ventures include the recently launched Corventis, which sells a sensor-based patch that detects the volume of fluid in a person with congestive heart failure and notifies her when it’s time to take a diuretic. PhiloMetron plans to spin off another startup company to market a calorie monitor, with a product on the market in 18 months. Drinan envisions the product being sold through health-care professionals or personal trainers, or at gyms. But the system will cost a pretty penny: somewhere between $100 and $400, sold as a kit with multiple patches included.

“There’s 1.6 billion people in the world who are overweight, and approximately 600 million of them are obese, so there’s consumer applications all over the place here–for everything from weight management to part of disease-management programs, to consumer applications for fitness and wellness,” says Jones of Qualcomm.

Eric Topol, director of the Scripps Translational Science Institute, in San Diego, and a practicing cardiologist, is interested in the device as a way to help keep his patients on track. He says that the technology is not only possible, it’s reality: “Digestion and metabolic activity affects tissue conductance, and this can be detected via appropriate sensors worn on the skin.”

Topol is interested in putting together a randomized clinical trial to see if the device can help people reverse type 2 diabetes, or help prevent progression to the disease in the first place. “I’m not suggesting that this is going to cure the obesity epidemic,” he says. “[But] I think it has great potential–if it works and it’s validated–to make an impact in the most common public-health problems today.”