Are Your Wearable Device Metrics Really Accurate?
Smartwatches like the Apple Watch, Fitbit, and Samsung Galaxy Watch promise to track everything from heart rate and blood oxygen levels to sleep quality and calorie burn. But how reliable is this data?
As a technology researcher who has studied wearables for over a decade, I’ve found that while these devices offer valuable health insights, they also have critical limitations—some of which could impact your health decisions.
Here are 5 surprising truths about wearable tech that manufacturers don’t always highlight.
1. Your Step Count Isn’t Always Accurate
✅ What you think it measures: The exact number of steps you take.
❌ Reality: It’s an algorithmic estimate based on wrist movement.
- Wearables use accelerometers to detect motion—not actual steps.
- Fast wrist movements (like typing or waving) can falsely register as steps.
- Walking in place or pushing a stroller may not count if your wrist stays still.
Pro Tip: For better accuracy, wear your device on your dominant wrist and calibrate it in your settings.
2. Skin Tone Can Affect Sensor Performance
✅ What you think it does: Tracks blood oxygen (SpO2) and heart rate equally for all users.
❌ Reality: Darker skin tones can reduce accuracy due to how light-based sensors work.
- Photoplethysmography (PPG) sensors use green LED lights to detect blood flow.
- Studies (and lawsuits) show lower accuracy for people with melanated skin.
- Apple and Fitbit acknowledge these limitations in fine print.
Workaround: If you have darker skin, check manual pulse readings for critical health data.
3. Your Location Data Might Not Be Private
✅ What you think happens: Your fitness data stays private.
❌ Reality: Many apps sell anonymized data to third parties.
- Strava’s 2018 heatmap accidentally revealed secret military bases via user jogging routes.
- Data brokers buy and sell health and location trends from wearables.
- Free fitness apps are the biggest offenders in data sharing.
How to Protect Yourself:
✔ Disable location sharing in app settings.
✔ Use fake birthdates/weight in non-essential apps.
✔ Opt out of data-sharing agreements when possible.
4. Consumer Wearables ≠ Medical Devices
✅ What you think: “My Apple Watch ECG is as good as a doctor’s.”
❌ Reality: Most wearables are not FDA-approved for diagnosis.
- Apple Watch ECG is cleared for atrial fibrillation detection—but not heart attacks.
- Sleep trackers estimate restfulness but can’t diagnose sleep apnea.
- Calorie burn estimates can be off by 20-30%.
When to Trust Your Device:
✔ For general trends (e.g., resting heart rate over time).
❌ For medical decisions—always consult a doctor.
5. Wearables Can’t Predict the Future
✅ What you think: “My Oura Ring can tell me if I’m getting sick.”
❌ Reality: They detect changes in baseline, not future illnesses.
- “Symptom radar” features look for unusual heart rate or temperature shifts.
- They can’t diagnose COVID, flu, or infections—just note anomalies.
- False alarms are common (e.g., from alcohol, stress, or poor sleep).
Best Use Case: Track long-term trends, not acute health events.
Final Verdict: Should You Trust Your Wearable?
✔ Yes, for trends & motivation—great for fitness and general wellness.
❌ No, for medical-grade accuracy—always double-check critical data.
Key Takeaways:
🔹 Steps are estimates—not exact counts.
🔹 Sensors work better on lighter skin—check manual readings if needed.
🔹 Your data may be sold—adjust privacy settings.
🔹 Not a doctor replacement—use wearables as supplements, not substitutes.
🔹 No fortune-telling—they detect patterns, not future health issues.
By understanding these limitations, you can use wearables smarter—without falling for marketing hype.
