You wake up, check your wrist, and get a score. Recovery 42%. HRV down. Sleep "fair". It can shape your whole mood before you've had a coffee.
So how accurate is it? The honest answer: it depends on what's being measured, and when.
The short answer
Wearables are good at some things and weaker at others.
- Resting heart rate and HRV overnight: generally the most reliable. You're still, so the sensor gets a clean signal.
- Heart rate during exercise: less reliable on the wrist, especially with fast arm movement, weights or intervals.
- Sleep stages: an estimate. Devices are reasonable at telling asleep from awake, but less precise about which stage you're in.
- "Readiness" or "recovery" scores: each brand's own formula. Useful as a nudge, but not a medical measurement.
Chest strap, watch or ring?
A chest strap reads the heart's electrical signal directly, like a simple ECG, which is why it's treated as the most accurate option at home. Watches and rings use light to detect pulse through the skin. That works well when you're still, which is why overnight readings are their strongest point.
When researchers compare devices properly, using the same time window and method, some wearables match an ECG very closely overnight. The catch is that different brands measure at different times of night and average differently, so two devices can give you two different numbers and both be "right".
The questions people ask most
Is HRV the same as resting heart rate? No. Resting heart rate is how many times your heart beats a minute. HRV is the variation between beats. They often move in opposite directions: when you're run down, heart rate tends to rise and HRV tends to fall.
Night or morning: which reading is better? Either can work. What matters is measuring the same way at the same time, so you're comparing like with like.
Should my HRV keep going up? No. It moves up and down with life. A stable baseline is a good sign. Chasing a higher number every week isn't the goal.
My friend's HRV is double mine. Is something wrong? Almost certainly not. HRV varies hugely between people and falls with age. Compare you with you.
How to use it without being ruled by it
- Look at weekly trends, not single mornings.
- Check how you actually feel before you look at the score.
- Use the data to spot patterns, like late nights, alcohol or hard weeks, then act on the pattern, not the number.
- If the score makes you anxious, take it off for a week. Your body will still be there.
Your watch isn't lying. But it isn't the whole truth either. You are the other half of the data.
The Toolkit
Picks that earn their place. Each solves one specific problem, and none is essential.
- Chest-strap heart rate monitor: the most accurate home option, especially for workouts. Wellness & Sleep picks
- Smart ring: comfortable overnight, good for spotting your own patterns. A guide, not a diagnosis. Wellness & Sleep picks
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Sources
- Shaffer & Ginsberg (2017). An overview of heart rate variability metrics and norms. Frontiers in Public Health.
- Physiological Reports (2025). Accurate comparison of wearables requires contextual equivalence.
- HRV4Training. The ultimate guide to HRV: common misconceptions.
Written by The Robots & Co. Edit. Our team brings a background in nursing, fitness and nutrition to everything we curate.
This article is general information, not medical advice. If you have concerns about your heart or your health, speak to your GP.