I am a self-confessed data nerd. I wear a smartwatch every single day. I track my runs, I monitor my recovery, and I love seeing my trends over time.
But recently, I have noticed a worrying trend in the Emergency Room.
Patients aren’t just coming in because they have chest pain. They are coming in because “my watch told me my oxygen dropped to 89% at 3 AM” or “my heart rate variability is lower than usual.” They are terrified, convinced that their device has detected a silent killer.
We have entered the era of the Quantified Self. We have access to more biological data than any generation in history. But here is the catch: Data without context is just anxiety.
So, let’s strip away the marketing hype. As a doctor, here is what I actually think about the sensors strapped to your wrist—what works, what fails, and what you can safely ignore.
❤️ The ECG Feature
Verdict: A potential lifesaver (for the right person).
The ability to take a single-lead ECG (electrocardiogram) on your wrist is arguably the most impressive medical achievement in consumer tech. It is FDA-cleared to detect Atrial Fibrillation (AFib), an irregular heart rhythm that is a major cause of strokes.
How it works:
By touching the crown or bezel of the watch, you complete an electrical circuit across your chest (from your left wrist to your right finger). The watch effectively takes a “snapshot” of your heart’s electrical activity.
✅ Who needs this?
- People over 65: The risk of “silent” AFib increases significantly with age. Catching it early allows us to start blood thinners and prevent strokes.
- People with palpitations: If you feel your heart “skipping a beat” or racing, capturing it on your watch can help your cardiologist make a diagnosis much faster than waiting for a 24-hour Holter monitor.
- History of AFib: Excellent for monitoring “burden” (how often you are going into AFib).
⚠️ Doctor’s Note: It cannot detect a heart attack. If you have chest pain, ignore your watch and call 911. A “Normal Sinus Rhythm” notification does not mean your arteries are clear.
💨 SpO2 (Oxygen) Monitoring
Verdict: Unnecessary anxiety fuel. Turn it off.
I will be blunt: This is the feature that sends the most healthy people to my ER unnecessarily.
The Science Gap:
Medical-grade pulse oximeters clip onto your finger and shine light through the fingertip. Smartwatches try to read oxygen by shining light onto the top of your wrist (reflectance pulse oximetry). It is notoriously difficult to get right outside of a lab setting.
Why you get false alarms:
- Sleeping on your arm: Compresses blood flow, causing a false low reading.
- Temperature: If your bedroom is cold, blood vessels in your skin constrict, dropping the reading.
- Motion: Moving during the measurement confuses the sensor.
- Loose Fit: Ambient light leaking in ruins the data.
I have seen healthy marathon runners panic over a reading of 88% when their lungs are perfectly fine. Unless you have severe COPD or acute COVID pneumonia, spot-checking your oxygen is medically useless and psychologically harmful.
🏃 Heart Rate Tracking
Verdict: Powerful tool, but context is everything.
Heart rate data is fantastic for one specific purpose: Exercise Physiology. But it is terrible for anxiety management.
✅ The Good Use
Zone Training: Knowing if you are in Zone 2 (Fat Burn) or Zone 5 (VO2 Max) helps you train smarter, not harder.
Resting Heart Rate (RHR): Seeing your RHR drop from 75 to 60 over a few months is the best objective proof that your cardio is improving.
❌ The Bad Use
The Anxiety Loop: You feel stressed. You check your watch. “Omg, my HR is 100.” You get scared. Adrenaline spikes. Your HR goes to 115. You panic.
Advice: Hide your heart rate from your main watch face. Check it after a workout, never during a panic attack.
💤 Sleep Tracking
Verdict: Helpful for the chaotic, optional for the routine.
I personally use sleep tracking. Working shifts in Emergency Medicine means my circadian rhythm is constantly under attack. I use the data to prioritize recovery on my days off.
The Rise of “Orthosomnia”
There is actually a new medical term for this: Orthosomnia—insomnia caused by the obsession with getting “perfect” sleep data.
If you wake up feeling rested, but your app says “Sleep Score: 65 – Poor,” how do you feel? Suddenly, you feel tired. You feel like you failed. That is the placebo effect working in reverse (the “nocebo” effect).
Use sleep tracking only if:
- You are actively trying to change a habit (e.g., seeing how alcohol destroys your REM sleep).
- You suspect Sleep Apnea (look for frequent “awake” spikes).
- You work shifts and need to manage recovery.
Otherwise? Trust your body. If you feel good, you slept well. End of story.
Common Questions from Patients
Is the Apple Watch ECG accurate?
Yes, for what it does (detecting AFib in a single lead), it is remarkably accurate and FDA-cleared. However, it cannot detect heart attacks, ischemia, or other structural heart problems.
Should I wear my smartwatch to bed?
Only if you are using the data to change a behavior (like going to bed earlier). If checking your “Sleep Score” makes you anxious in the morning, take it off. Comfort and low anxiety are better for sleep than data.
My watch says my Low Cardio Fitness is poor. Should I worry?
Not necessarily. This is an estimate of your VO2 Max. It can be skewed by GPS errors, running on hills, or loose straps. Use it as a rough trend line, not a medical diagnosis.
The Bottom Line
Wearable tech is a tool, not a diagnosis. If your watch is motivating you to move more and sleep better, keep it. If checking your wrist is the first thing you do when you feel stressed, it might be time to take a break.
You are the expert on how you feel. The watch is just an accessory.
