Smartwatches have improved our lives a lot. Their built-in health tracking has made health data accessible to more people than ever before, making us all a little more cognizant of our physical condition. That said, new research says we should not take that data at face value.
Researchers at the University of Michigan and Hope College dug into how accurate our trusted smartwatches really are in a new review published in the journal Sensors, and the results are a mixed bag.
What can you actually trust?
The study found that basic health metrics like resting heart rate hold up well, staying within a couple of beats per minute of the real thing under normal conditions. Sleep tracking is also solid at telling you whether you’re asleep or awake, with over 90% accuracy. But once you get into specific sleep stages like REM or deep sleep, accuracy takes a massive hit, sometimes dropping as low as 50%.
So where do things fall apart?
Things got even worse when researchers started verifying the more complex features. Calorie burn estimates can swing by 10 to 20%, and VO2 max numbers vary depending on how fit you already are. Blood pressure tracking, hydration monitoring, and blood glucose readings are still very much a work in progress. In fact, the FDA has specifically warned against relying on smartwatches or smart rings for glucose monitoring altogether.
The big takeaway from this research is that most of these numbers are modeled estimates built from algorithms, not direct measurements of what’s happening inside your body. Smartwatch data is useful for spotting trends over time, but you shouldn’t treat every number as gospel, especially anything medical.
So the next time your watch flashes a warning or claims one of your health metrics jumped overnight, take it with a grain of salt. It’s a helpful nudge, not a lab report. And if you are feeling unwell, it’s best to visit a doctor and get proper tests done rather than relying on your smartwatch data.
