Measuring blood pressure with a smartwatch: what the watch can really do
A watch on your wrist does not measure pressure – it extrapolates it from light signals. Why this difference determines whether a number is of any medical value.
Since smartwatches and fitness rings started providing information on blood pressure, a new question has been coming up in doctors' surgeries: my watch says everything is fine – do I still need to measure with a cuff at all?
The answer depends on a technical detail that is rarely made clear in product descriptions: A watch on your wrist does not measure pressure. It estimates it. What this means in practice can now be backed up with figures.
What a smartwatch actually measures
Almost all wearables work with photoplethysmography, PPG for short. Small LEDs shine light into the skin, and a sensor records how much of it comes back. Because the blood volume in the tissue changes with every heartbeat, the reflected light fluctuates too. From this light curve, an algorithm calculates heart rate, oxygen saturation – and, on some devices, an estimate of blood pressure.
What is measured is light, not pressure. The blood pressure value is only produced in the next step, by a computational model.
Why estimated is not the same as measured
A conventional upper arm monitor takes the opposite route. It inflates a cuff until the blood flow in the artery stops, and then releases the pressure in a controlled way. The point at which the blood starts flowing again is the systolic value; the point at which the flow sound disappears is the diastolic value. This is a physical measurement of a physical pressure. The method goes back to Riva-Rocci and Korotkoff and has been the medical reference point for over a hundred years.
An optical model, by contrast, derives the pressure indirectly. It usually needs calibration against a cuff device, it is sensitive to arm position, skin type, tattoos, movement and temperature – and its calibration becomes outdated over time. An estimate may be right in many cases. That does not make it reliable.
What research says about the hit rate
At the end of 2025, several manufacturers introduced features that flag possible signs of high blood pressure over a period of about 30 days – the best known being the Apple Watch hypertension notifications. It is important to know: These features do not provide blood pressure values. They give a notification – or they don't.
An analysis published in 2026 in the Journal of the American Medical Association extrapolated what this would mean for the population. The result: Around 59 per cent of adults with undiagnosed high blood pressure would receive no notification. At the same time, around 8 per cent of people without high blood pressure would receive a notification that is not confirmed.
This leads to a practical rule worth remembering: a notification from your watch is a reason to measure again carefully. The absence of a notification is not an all-clear.
What a wearable is still good for
This is not an argument against wearables as such. They are strong at what they were built for: heart rate throughout the day, resting pulse over time, sleep phases, activity, reminders. Some models detect atrial fibrillation remarkably reliably, because they do not need a pressure model for this, only the time interval between two heartbeats – and an optical sensor really does capture that directly. How accurate this is and what such a notification is worth is explained in Atrial fibrillation and smartwatches: what the sensor really recognises.
The fault does not lie with the device. It lies in the expectation that a screening notification does the same job as a measurement.
What even a good single measurement does not show
The second blind spot affects all devices, even the best upper arm monitor. Systole and diastole describe two points of a process that continues without interruption. What happens between two measurements – at night, under strain, in the minutes after getting up – remains invisible.
Yet precisely this range of fluctuation is medically relevant. If you measure once a day, you see a snapshot; if you see the course, you recognise patterns. It is the difference between a photo of a river and knowing whether the water level is rising or falling.
What a reliable measurement at home looks like
- Use a validated upper arm monitor – validated devices are listed by the professional societies.
- Sit quietly for five minutes, do not talk, cuff at heart level.
- Two measurements one to two minutes apart, write both down.
- Morning and evening, over seven days – it is the average of this series that counts, not the single value.
- Treat notifications from your smartwatch as a reason to measure again, not as a result.
How to avoid the most common mistakes is explained in detail in our article Measuring blood pressure correctly: 7 mistakes that distort your readings. We explain the terms relating to pulse and pressure curves in our glossary.
It cannot be done entirely without a device – why feeling your pulse and interpreting symptoms do not produce a blood pressure value is explained in Measuring blood pressure without a device – is it possible? And if you do want to add a wearable: Buying a blood pressure wearable: 7 questions before you decide.
When you should seek medical advice
If your watch gives a notification of possible high blood pressure, measure carefully for a week and discuss the values with a doctor. The same applies to persistently elevated home readings of 135/85 mmHg or above, to strongly fluctuating values and to symptoms such as dizziness, visual disturbances or chest pain.
And if the watch reports nothing but you feel unwell: trust that feeling, not the missing signal.
How to describe your symptoms so your doctor can actually work with them
Five steps for your next doctor’s appointment – plus a printable template for noting down your observations.
This is how it usually sounds
“I felt strange again last night. A kind of stumble, and it gave me a fright.”
“Let’s keep an eye on it.”
The guide shows you how to describe it instead and which questions to ask. What is usually missing are the numbers from exactly those two minutes – and those are what the BPER records, beat by beat.
Frequently asked questions
Can a smartwatch really measure blood pressure?
No. Common wearables record optical signals and derive an estimate from them. No physical pressure measurement takes place. Some models give a notification of possible signs of high blood pressure over a period of about 30 days, but no blood pressure values.
How reliable are smartwatch hypertension notifications?
An analysis published in 2026 in the Journal of the American Medical Association concludes that around 59 per cent of adults with undiagnosed high blood pressure would receive no notification. Around 8 per cent of people without high blood pressure would receive a notification that is not confirmed.
My watch reports nothing – does that mean my blood pressure is fine?
Not necessarily. The absence of a notification does not rule out high blood pressure. If you belong to a risk group or have symptoms, measure regularly with a validated upper arm monitor regardless.
What are smartwatches useful for when it comes to the cardiovascular system?
They are well suited to heart rate, resting pulse over time, activity and sleep. Detection of atrial fibrillation also works reliably on some models, because it only requires evaluating the time intervals between heartbeats.
How reliable is blood pressure measurement with a smartwatch?
As a stated value: not reliable enough to replace a cuff. Optical methods estimate pressure from the pulse wave and drift further from the last calibration over time. As pattern recognition over weeks, on the other hand, they can be useful – but that is something different from a measured value.
How does a smartwatch calculate blood pressure?
Using photoplethysmography: an LED shines into the skin, a sensor measures the reflected light and, from it, the shape of the pulse wave. From features of this curve, an algorithm estimates a pressure value, matched against an earlier calibration on a cuff device. The pressure itself is never measured – it is derived.
How does blood pressure measurement with a watch work?
A watch without a cuff does not measure, it estimates. There are a few watches with an air bladder in the strap – these have a real, if very small, cuff and do actually measure. The difference is crucial: only where pressure is built up against the artery do you get a measured value rather than an estimate.
How reliable is blood pressure measurement at the wrist?
Much more reliable than a watch without a cuff, because a wrist monitor has a real cuff. However, it is more sensitive to posture: the wrist must be at heart level, otherwise the value will deviate systematically. For people with a very muscular upper arm, it is often the more accurate choice.
Understand your blood pressure – a little more every week
One article a week: clear, reviewed, no advertising promises. Free to your inbox.
You will receive a confirmation email (double opt-in). Unsubscribe at any time with one click. Our privacy policy applies.
Sources
- JAMA 2026: Impact of a Smartwatch Hypertension Notification Feature for Population Screening (DOI 10.1001/jama.2025.26925)
- University of Utah Health: New Study Reveals Gaps in Smartwatch's Ability to Detect Undiagnosed High Blood Pressure, 2026
- Deutsche Hochdruckliga e. V. DHL: Blutdruckmessgeräte mit Prüfsiegel
- European Society of Hypertension: 2023 ESH Guidelines for the management of arterial hypertension
This article is for general information only and does not replace a medical diagnosis or treatment. If you have symptoms or questions about your treatment, please consult your doctor.