One of today's hottest exercise devices fits in your pocket, costs about $25 and is so simple a child can use it.

Electronic pedometers have become increasingly popular "movement motivators" in health promotion programs, including weight loss clinics, corporate fitness centers and physical education classes. The palm-sized gadgets clip onto your waistband and record the number of steps you take, with more sophisticated models also calculating distance covered and calories burned. The goal for good health, many experts say, is to accumulate 10,000 steps per day.

"People love it because they get immediate feedback on how active, or inactive, they are," says David Bassett, an associate professor of exercise science at the University of Tennessee, Knoxville. Unlike old-style mechanical pedometers, the newer electronic versions are extremely accurate, says Bassett, whose study testing five popular models appeared in the journal Medicine and Science in Sports and Exercise.

The Japanese have used electronic pedometers for more than a decade to help counteract sedentary lifestyles, Bassett notes. Nicknamed "manpo-kei," which means "10,000 steps meter" in Japanese, the devices were brought to the United States in the mid-1990s by exercise scientists who used them to determine daily activity levels in research studies.

"Most researchers had been using questionnaires to record low to moderate activity levels," he notes. "But their accuracy was questionable because people often can't remember how many flights of stairs they climbed or how often they got up and walked." In contrast, electronic pedometers are an extremely accurate means of recording daily life activity. Study participants found the devices so helpful that, over the last several years, pedometers have become an increasingly popular tool for helping motivate people to become more active.