context: Combine a highly evolved pedometer with a mini computer and a virtual coach and what do you have? A fitness tracker. These high-tech gadgets contain sensors that pick up data about your body (heart rate), activity (steps taken and calories burned), sleep, and more. This kind of insight allows you to make smart choices -- everything from ramping up the intensity of your workouts to gaining the motivation to drop extra pounds. With dozens on the market, how should you choose? Each device has its own combo of special features. Be on the lookout for features like these: Step counter. Most devices show you the number of steps you take and how many miles that equals. If walking or running is your main exercise, this is the feature you'll use most. Shop for devices that ask for the length of your footstep or âcadence.â They'll provide the most accurate information. Calories burned. Using your weight and gender, fitness devices can calculate the calories you burn in a day. The harder you exercise and the more you move throughout the day, the more calories you burn. Be aware, some devices only record the calories you burn during exercise. Others record activity all day, like washing dishes, folding laundry, and sleeping. Be sure to look for devices that ask for your weight and gender to get the most accurate results. Sleep tracker. A few devices track sleep. While they're not accurate enough to diagnose sleep disorders, they do give you an indicator of how much sleep you get vs. how much you toss and turn. The built-in reporting can help you spot patterns. Getting enough sleep can help you lose weight. Too little sleep may lower your metabolism and increase your appetite. Making sleep a priority may also lower your risk of obesity, type 2 diabetes, and heart problems. Heart rate monitor. Want to get the most bang for your buck? If so, monitoring your heart rate will help by gauging your exercise intensity in the moment. This information will help you know when to rev up or slow down and recover. Some devices even sense your body temperature and sweat to gauge how hard you're exercising. If you have heart problems or take certain blood pressure medicines, ask your doctor if checking your heart rate during exercise is a good way to measure your exercise intensity. Stair counter. Some devices have an altimeter to count the flights of stairs or hills you climbed. If you're a hiker or outdoor enthusiast, you'll appreciate the data you get from an altimeter. It gives a more accurate reading of how hard you're working and how many calories you've burned. GPS. Some gadgets have built-in GPS to estimate your speed. They also show you a map of your route. GPS is especially helpful with exercises that the typical accelerometers or pedometers in fitness devices don't track well, like biking. Water resistance. Some trackers are water-resistant, so you can shower with them on, but not swim. A few specialty devices, like swimming watches, are fully waterproof. These time your laps, count strokes, and calculate speed and distance. A few trackers combine swim tracking with bike tracking, too. They're ideal for triathletes. Sync technology. Want updates on the go? Look for devices that sync wirelessly. Other devices will require you to plug into the jack on your smartphone or to your computer. On-device display. A few devices offer a display that provides some data in the moment. Otherwise, you will need to sync with your phone or computer. For devices with Bluetooth, this isn't such a big deal. But if you have to take the device off to get the data from your phone, it could get tricky when monitoring workouts in the moment. If you have to sync to your computer, you pretty much have to wait until your workout's over. How your new fitness tracker collects and shares data isn't the only thing to consider. Size. Trackers come small enough to clip to your waistband or bra. Some can fit in your pocket. Others are worn like watches. Make sure you like the design, and that it feels comfortable. Gadget friendly. Make sure the device is compatible with your smartphone or computer. You might also want to check if it will sync to fitness and food tracking apps like Lose It! or My Fitness Pal. Social. Some fitness devices allow you to "friend" other people who use the same device, just as you would on Facebook. Once connected, you'll see each other's steps on the device's app or web site. This can help motivate you to take your activity to the next level, especially if you have a competitive spirit. Thankfully, all have privacy settings so your friends only see what you want them to see! Some fitness devices even offer caller ID, text messaging, email capabilities and more. Cost. Most devices range from $30 to over $200. Watch for hidden expenses. A few require a monthly subscription to the web site if you want to see your data.