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Smartwatch data accuracy for heart rates, etc.
© Andrey Popov |

Sorry, your smartwatch isn’t as accurate as you think

Sensors in today’s smartwatches can detect your heartbeat, track how you sleep and even monitor blood oxygen levels. If Apple gets its way, your watch will be able to track your blood sugar (and possibly send reports about it to your doctor).

If you’ve ever wondered, “Just how accurate are these smartwatch readings?” You’re far from alone, so I took a look. Smartwatches and fitness watches have some serious flaws you should know about.

Paging Dr. Watch

It turns out cramming a bunch of sensors into a tiny watch doesn’t create the most legit results — who knew? If you’re seeing spikes or drops in readings for sleep states or blood oxygen levels, don’t panic — it’s happening to everyone.

  • Sensors have problems with skin tone: It’s gotten so bad users have filed a lawsuit against Apple because blood oxygen sensors don’t work correctly on dark skin. Yikes! However, research indicates this may be a problem with many blood-oxygen sensors.
  • Watches don’t reach medical levels of accuracy: High-grade studies are limited, but this one done on Garmin fitness watches found that the watches could measure neither energy expenditure nor blood oxygen levels with enough accuracy to make medical decisions.
  • Step counters and calorie trackers are easily fooled: Smartwatches like the Apple Watch 6 and Fitbit Sense stink at measuring calories burned and can struggle to define steps walked. And don’t get me started on how vague sleep tracking can be!

OK, so smartwatches are only helpful for very guessy guestimates. But what can we do to make them better?

Take your health in stride

Here are a few figurative steps I think all smartwatch users should take while getting in their literal steps (plus a free play on words!).

  • Size your watch for your wrist: Many accuracy problems are caused by loose-fitting watches that slip around on your arm. Buy one you can adjust.
  • Focus more on heart rate than steps or calories. Your pulse is right there, so it’s no surprise watches are more accurate about heart rate than almost anything else. 
  • Don’t get stressed out over readings: Ironically, that stress will increase your heart rate and other vitals. Even worrying about sleep tracking can cause inadequate sleep (doctors call it orthosomnia). Don’t think of readings as hard numbers but rather general brushstrokes about your health picture.
  • Watch readings over time instead of individual numbers: Those charts and graphs are more helpful than going number by number.
  • Visit a doctor if you’re worried: Don’t waste time or energy obsessing over what your watch tells you. If you’ve got a serious concern, make an appointment like a grown-up.

My smartwatch picks

If you don’t have a smartwatch yet, here are a few good ones:

🤣 Having a smartwatch is great. On the one hand, you have something you can use to answer texts and stuff; on the other hand, you don’t. (Was that a groan I heard?)

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