Measuring blood pressure without a device – is it possible?

The question comes up in every search engine: can blood pressure be determined without a monitor? The short answer is no. The longer answer is more interesting – because although you cannot obtain a reading without a device, you can observe a number of things that are medically relevant.

Blood pressure is a physical quantity. It describes the pressure that blood exerts on the vessel wall, measured in millimetres of mercury. To determine it, the vessel has to be compressed from the outside with a defined counter-pressure, while observing when blood flow stops and when it starts again. That is exactly what a cuff does. Without this counter-pressure there is no reference point – and without a reference point there is no number.

What your pulse reveals – and what it does not

The pulse you can feel at your wrist or neck tells you about rate (how often the heart beats) and rhythm (whether it beats regularly). Both are valuable: an irregular pulse can be an indication of atrial fibrillation and should be checked by a doctor.

What your pulse does not reveal is the pressure. A strong pulse does not mean high blood pressure, and a weak one does not mean low blood pressure. How the pulse feels depends on the position of the vessel, the thickness of the tissue above it and the sensitivity of your own fingers.

The widespread assumption that pulse and blood pressure rise together is not true either. Although both are controlled by the same nervous system, they regularly diverge. How pulse, systolic and diastolic values are related is explained in Pulse pressure: what the gap between the upper and lower reading means.

The thing about symptoms

A persistent misconception is that you can feel when your blood pressure is too high. Headaches, nosebleeds, a red face, ringing in the ears – all of these are regularly interpreted as signs.

In fact, high blood pressure remains symptom-free for years. That is the real reason why it is taken so seriously as a risk factor: it causes damage without making itself known. Conversely, headaches have dozens of causes, most of which have nothing to do with blood pressure.

Symptoms usually only appear at very high readings – or with a rapid rise. If you rely on how your body feels, you miss the years in between. This is exactly why the cuff cannot be replaced.

Smartphone apps without a cuff

There are apps that claim to derive a blood pressure reading from the phone's camera, from placing a finger on the sensor or from your face in the front camera. They are usually based on photoplethysmography – an optical method that captures changes in volume in the tissue.

This signal contains information about the pulse wave. It does not contain a pressure value. What such apps display is an estimate from a model – and the model needs reference data that it does not have. For methods based on this technique, there is so far no product of this design validated to ISO 81060-2.

The same limitation applies to smartwatches that work without a cuff. The connection is described in detail in Can a smartwatch measure blood pressure?, and why a preceding cuff measurement does not solve the problem in Calibrating wearables.

What makes sense without a device

Without a cuff you will not get a reading. But you can make observations that may justify a visit to the doctor:

• Feel your pulse rate and rhythm. Place your index and middle fingers on the thumb side of your wrist, count for 30 seconds and double it. Pay attention to any irregularities.
• Note dizziness when standing up – an indication of orthostatic drops in blood pressure.
• Snoring at night with pauses in breathing – a common and often overlooked driver of raised readings, see Sleep apnoea and high blood pressure.
• Everyday fitness – shortness of breath when climbing stairs that was not there before.

This does not replace a measurement. But it is a more honest basis than an app number that looks like a reading but is not.

The simplest way to a real reading

A validated upper-arm monitor costs less than most fitness bands. In Germany, pharmacies will measure your blood pressure free of charge, and many GP practices will also do so without an appointment. When a reading is needed, this route is quicker and more reliable than any alternative without a cuff.

How to measure correctly is explained in Measuring blood pressure correctly, and when to measure in When should you measure your blood pressure?.

When you should seek medical advice

• If you feel an irregular pulse
• If you have recurring dizziness, especially when standing up
• If your fitness is declining or you have new shortness of breath
• If you have not had your blood pressure measured for years

In case of sudden severe headache, chest pain, speech or visual disturbances or one-sided paralysis: call the emergency services on 112 immediately.