Keeping tabs on all the calories your body burns—at rest, working out, and living life—used to mean joining a research study, becoming a Biggest Loser contestant (they wear calorie monitors on their arms), or shelling out big bucks for a high-tech, bulky armband.

No longer. GoWear Fit, a sleek monitor, tracks motion, steps, sweat, skin temperature, and heat flux from your muscles, then calculates the input with an equation that takes into account your age, gender, height, weight, and other personal details to reveal your daily calorie expenditure. Worn on your upper arm, the nifty device collects data that you download to your computer via a USB cable, and the data is whisked to a password-protected webpage that displays your calorie information, total daily activity, total daily steps (from running or walking), and sleep time. Manufactured by BodyMedia—the same company that makes the Bodybugg, used by Biggest Loser contestants—the armband costs $199 plus monthly online costs ranging from $7 to $13. For on-the-spot feedback, a $99 display you wear on your wrist will track your data in real time.

Exercise researcher Stephen Yang, PhD, an assistant professor of physical education at State University of New York College at Cortland, says this innovative armband takes the guesswork out of one side of the weight loss equation. "Until recently, mainly research labs used devices that measured calorie burn this way," he says. "Seeing the numbers can be a real motivator and will help keep you from missing workouts." Use the GoWear Fit to figure out how much additional activity you need to burn an extra 500 calories a day. If you keep up that effort, you should drop about a pound a week.

Sari Harrar is a health and science writer living in Pennsylvania.