Photo: Adam Voorhes

As a gadget guy, I've gone through several wearable activity trackers over the years. My first love was the Fitbit. Then I moved on to the Nike+ Fuelband, and now I'm trying the Up by Jawbone. I've even worn two devices at the same time to test how well their results matched up at the end of each day. Guess what? They didn't. The truth is, many of these gizmos can be inaccurate—but they're consistently inaccurate, which means you can still gain valuable information by looking at patterns in your behavior, even if the numbers aren't spot-on. So while I may not know the exact number of steps I took today, I know how I did compared with yesterday or last week, and that's real data I can use. But don't get swept up in trying to track everything—you'll drive yourself crazy. Here's what to focus on and what you can skip.

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If you're going to monitor only one thing, this is it: Without adequate rest, your whole body suffers. The best way to measure the quality and quantity of your sleep is with brain wave technology, but that's not yet practical outside a laboratory. Some of today's trackers offer only approximate results based on how restless you are during the night, so you're not going to get perfect data. Research has found that motion-tracking devices can overestimate how long and how well you've slept. But if you keep track of your uneasy nights, you may be able to pinpoint the daytime factors that could be throwing off your sleep. Bonus: Some devices allow you to set a sleep goal and will send you an alert when it's time to turn in.

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Many trackers automatically set your daily goal at 10,000 steps. And for good reason: One study found that women who consistently walked about that far (give or take 400 steps) lowered their systolic blood pressure by an average of 11 points over 24 weeks. Use any type of pedometer to find the average number of steps you're currently taking, and then challenge yourself to add an extra 1,000 (that's only half a mile!) each day until you reach 10,000.
Heart Rate

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WORTH IT: Heart Rate

I was initially skeptical about the heart rate monitors embedded in fitness trackers because I believed the only way to get an accurate number while exercising was to strap on a chest monitor that reads the heart's electrical activity. But some of the newest devices use a method that comes close: They shine a light at the blood vessels in your wrist, and a sensor detects each surge in blood flow that corresponds to a heartbeat. The data can help you track your heart rate while you work out and while at rest. Your resting heart rate should be 60 to 100 beats per minute, though physically fit people tend to have lower resting rates than those who don't work out.
Blood Oxygen

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DON'T BOTHER: Blood Oxygen Count

As companies add more bells and whistles, I've noticed that some trackers now include a feature that measures blood oxygen levels, which can give you an idea of how well your lungs are working. But unless you're a pro athlete or suffering from a breathing condition like sleep apnea, you really don't need this extra info. The data you'll get from the heart rate monitor are a good enough gauge of your overall fitness.

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DON'T BOTHER: Stress Level

Believe it or not, there are now gadgets that can supposedly monitor your stress level with the help of sensors that track your breathing. But do you really need a device to tell you how tense you feel? Sometimes it's better to ignore the stats and listen to your body instead. You'll probably feel calmer if you just give yourself a chance to unplug.