Where to start
Start from the question rather than the device. If you have one number you do not understand, read the normal resting heart rate guide or the heart rate variability guide. If you want to know whether your nights are good enough, read how much sleep you need and then sleep stages.
If you want one habit, the sleep and measurement guides are the cheapest place to begin: how to improve sleep quality costs nothing, and how to measure your resting heart rate needs only a clock. If you are thinking of buying something, read the comparisons of fitness trackers, smart rings and sleep trackers after you have decided what question you want answered.
What a wellness device can and cannot do
A band, ring or watch estimates your heart rate with light sensors on the skin, and estimates sleep from movement and pulse. Those estimates are useful for following your own pattern at home. They are not a diagnosis, they cannot rule a condition in or out, and they do not replace a GP or a pharmacist.
Oxygen readings and fitness scores deserve extra care. The blood oxygen guide and the VO2 max guide explain which of these figures a clinic measures directly and which a device only infers.
How to read a number from a tracker
Ask three things. What was it measuring, when was it taken, and how does it compare with your own recent weeks? A single reading after a poor night, a hard session or a coffee tells you little. A shift that lasts for weeks tells you more, and the heart rate zones guide shows how effort changes the figures you see.
Scores differ between brands because each company chooses its own formula, so a recovery score on one app cannot be compared with a readiness score on another. If you are weighing two systems, Oura against Whoop sets out what each reports and how, without declaring a winner.
How these guides are made
Every guide here starts from British sources, chiefly the NHS website, NICE guidance and the relevant British charities, and gives each figure a numbered source with the date it was read. A figure without a source is left out, and where a British source is silent the guide says so rather than borrowing a number from abroad. Product guides state what a category of device is designed to do, which criteria matter, and what a claim on a box can and cannot mean.
Health pages carry the line “Medical review in progress.” until a qualified reviewer has checked them, and no page names a reviewer before that has happened. Prices appear only on product pages and in the boxes that link to them, in pounds. Nothing here suggests that anyone other than you pays for a Chutex product, and these are wellness products, not medical devices.
When to get help
Call 999 in an emergency, such as chest pain, severe breathlessness, fainting or sudden weakness. Call NHS 111 for urgent advice that is not an emergency. For anything else that worries you about your heart rate or your sleep, speak to your GP.
All guides in this topic
Normal resting heart rate: what the BHF and NHS say, and how to check yours
The usual adult range, how to count your pulse, and which signs mean you should get advice.
Heart rate variability (HRV): what it is, what moves it and how to read a band
The gap between heartbeats, what shifts it, and what a wearable can honestly tell you.
How much sleep do you need? What the NHS says by age, and how to tell if you are short
Hours by age from the NHS, a way to check your own night, and the habits and signs worth acting on.
Sleep stages explained: light, deep and REM sleep, and what your tracker chart shows
The four stages, how a night is built from 90-minute cycles, and how far to trust a wrist chart.
How much deep sleep do you need? What UK sources say, and why your tracker may differ
The usual share of the night, what shortens it, and how to read a low deep sleep number on a wrist tracker.
How to improve your sleep quality: the habits UK health sources list, and how to test them
Eleven everyday habits, where UK sources agree and where they differ, and a fortnight test for your own sleep.
How to measure your resting heart rate: take your pulse at the wrist, step by step
Where to find your pulse, how long to count, a seven-day record sheet, and when a reading needs advice.
Heart rate zones: moderate and vigorous effort, maximum heart rate and bpm by age
The BHF’s moderate range, the talk test, three ways to estimate maximum heart rate, and a bpm table by age.
Normal blood oxygen level: what UK sources say, why oximeters can mislead, and when to get help
The usual 95 to 100% range, what limits a fingertip or wrist reading, and which symptoms mean urgent help.
VO2 max: what the number means, how it is measured, and how far to trust a watch
A plain guide to VO2 max, the British figures that exist, and the limits of every way of measuring it.
Best fitness trackers in the UK: a dated comparison, with the real three-year cost
Eight wearables side by side on prices read on 2026-10-16, plus what studies say about how accurate they are.
Best smart rings in the UK: a dated comparison of cost, sizing and accuracy
What rings cost to own, how sizing works, what studies say about accuracy, and when a band is the better fit.
Best sleep trackers in the UK: a dated comparison, and what the accuracy studies say
Wrist, ring, band and under-mattress devices side by side, with the limits of sleep stage tracking.
Oura vs WHOOP in the UK: cost, evidence and data rights, side by side
A ring and a band compared on what the makers state, what small studies found, and what UK data rules say.
Words you will meet on these pages
- Resting heart rate
- Your heart rate when you are calm and still, counted in beats per minute.
- Heart rate variability (HRV)
- The variation in time between heartbeats.
- Sleep stage
- A phase of sleep that a device estimates from movement and pulse.
- SpO2
- An estimate of the oxygen carried in your blood, shown as a percentage.
- VO2 max
- A measure of how much oxygen your body can use during hard effort.
- NHS 111
- The NHS service for urgent advice that is not a 999 emergency.
Frequently asked questions
Can a tracker tell me if I have a heart problem?
No. A tracker estimates a pulse for wellness use and cannot diagnose a condition. If you have symptoms, speak to your GP, and call 999 in an emergency.
Why does my sleep score differ between apps?
Each brand uses its own formula and its own sensors, so the scores are not comparable. Compare your own trend inside one app.
Which guide should I read first?
Read the one that matches your question: heart rate, HRV, sleep length, sleep quality, or a product comparison. Each links to the others.
Are the figures British?
Where a British source gives a figure, the guide uses it and dates the reading. Where none exists, the guide says so.