Wearable fitness devices are getting smarter. Here's what you can expect from the newest crop of trackers. 
Credit: Illustration: Andrew Lyons

Today's fitness trackers are a far cry from the earliest pioneers of the wearable tech world. These gadgets can still count your steps and your stairs, but now they can check your temperature, measure your heart rate, and even monitor your perspiration. For the step-seeking desk jockey, fitness trackers can help raise awareness about stretches of inactivity—people who spend long hours sitting have an increased risk of bone and organ damage.

All of these things make fitness trackers more popular than ever, and tech companies are working to make them technologically smarter, as well as more visually appealing. "Right now, we have a lot of plastic bracelets, which feel very sporty. We're moving toward a more fashionable place, where aesthetics aren't secondary to the technology," says Amanda Parkes, PhD, Chief of Technology and Research at the New York–based wearable tech firm Manufacture NY. "We have to create a product people want to wear not just when they're exercising because wearing these devices all day can provide a biometric, holistic picture."

If you're in the market for a fitness tracker or are looking to upgrade an old one, discover what today's wearable tech devices do—and what they don't.

The Four Things Fitness Trackers Can Do 

1. Count Your Steps: Most trackers have come a long way from the analog step-counting pedometers of yesteryear. Accelerometers, devices used to guide spaceflight, are now used in trackers to monitor how much and how intensely you're moving. Some fitness trackers display your step and activity numbers right on their tiny screens. Others require a Bluetooth connection with a smartphone or tablet to view the information.

The Downside: Although they're great guides, the numbers your device generates shouldn't be taken as gospel. They estimate based on the stats they gather and the information you provide. "Even if you know your heart rate and five or six other things about your body, you may not have any actual information that tells you whether you're healthy or not," Parkes says. "They can give you a series of measurements but not a real picture of your health."

2. Track Your Health: New wearable devices gather more info about your health than ever. Sensors for heart rate, perspiration, skin temperature, and even blood oxygenation provide you with real-time relays of how your body is performing. Many smartphone apps also have their own calorie-counting component or they link to a third-party app so the two apps can share information and adjust your daily calorie limit. It's an easy way to understand how many calories your exercise "earns" you.

The Downside: The algorithms used are only a guess. If you eat every calorie you "earn," you probably won't lose weight. "There's a difference between detecting activities accurately and calculating how many calories were burned," says Lucy Dunne, PhD, associate professor of apparel design and wearable technology at the University of Minnesota.

3. Monitor Your Sleep: Turn on the sleep mode, and the device will detect movement while you snooze. When you wake, it tells you how long you slept and how often you woke up. Some trackers can even act as an alarm, vibrating at a point in your sleep cycle when you're more likely to wake up feeling refreshed.

The Downside: These devices are sensitive but not enough to provide medically relevant feedback. "The better ones seem to be accurate in detecting sleep from wakefulness, but I would be skeptical of any that purport to do more, like distinguish stages of sleep," says Anays Sotolongo, MD, assistant professor of medicine at Rutgers Robert Wood Johnson Medical School. "If you track that you are getting eight hours but are still sleepy, maybe you should see a physician."

4. Provide Encouragement: Social networking is an extremely effective weight-loss tool. Many fitness trackers allow users to connect with a group to provide encouragement and real-time feedback for your goals. This is a powerful benefit of fitness gizmos: Research shows that social support can be one of the biggest driving forces behind weight-loss success. People who feel connected and know that their goals and choices are reinforced by people who care about them are more likely to stick to those goals.

The Downside: There really isn't one. On most apps, you can keep sensitive information like your weight private, and you can customize how much you share.