Smartwatches May Give False Reassurance On Blood Pressure Safety

Millions wear smartwatches that flash reassuring numbers for their heart rate and sleep. Some even warn if blood pressure spikes. New research suggests relying on these gadgets could leave millions falsely believing they are safe. That mistake might increase the risk of a heart attack or stroke.

About 16 million people in the UK have high blood pressure. Another five million may suffer from it without realizing, since symptoms often stay hidden. Consistently high force against artery walls strains the heart and vessels. This strain raises the danger of serious cardiac events.

Certain smartwatches promise to spot this problem. They do not measure pressure like a GP's cuff does. A medical cuff inflates around the upper arm to read artery pressure directly. Instead, these watches use wrist sensors to pick up pulses. An algorithm estimates blood pressure from that data. Movement or how the arm sits can distort those estimates badly.

Yet millions depend on them. Apple Watch users number 200 million globally. Huawei, Samsung, and Xiaomi devices serve more than 400 million people combined. A version of the Apple Watch released last year got approval from the US Food and Drug Administration for its hypertension notification feature. It uses an optical sensor that tracks wrist pulses with light.

High blood pressure changes how pulses travel through arteries. The watch hunts for these shifts over a period of 30 days. It builds an average reading to flag potential issues. But recent work in JAMA found worrying proof. The device missed more than half of those with undiagnosed high blood pressure. The NHS defines home readings above 135/85 as high. Ideal numbers sit between 90/60 and 120/80.

Experts at the University of Pennsylvania analyzed Apple's test data from 1,800 volunteers. They checked how often the watch got it right or wrong. Then they added separate US data from another 4,000 adults. That mix helped estimate who would get a warning if usage expanded widely. Results showed only 41 per cent of hidden high blood pressure cases triggered an alert.

The device performed better for people with healthy blood pressure. Still, it made errors there too. In 92 per cent of normal cases, no alert appeared as expected. Yet 7 per cent received a warning that their pressure was high. Thirty days of proper cuff monitoring had already confirmed their readings were fine. Apple says the feature is not meant to diagnose or treat hypertension.

This study follows a warning from last year by the American Heart Association. They stated smartwatches and similar wearables are not reliable enough for diagnosis yet. Dr Jordana Cohen, a hypertension consultant at the University of Pennsylvania, spoke on this point. She was part of the American Heart Association review team. 'Cuffless blood pressure devices are convenient and capable of frequent or continuous monitoring,' she noted. However, the speed of commercialisation has outpaced the science.

Readings from cuffless blood pressure devices lack the necessary validation to guide treatment decisions. Similar reliability problems have surfaced with smartwatch alarms for irregular heart rhythms. A 2020 study published in the Journal of the American Medical Informatics Association looked at 264 people who rushed to medical care after their Apple Watch flagged an abnormal heartbeat.

Atrial fibrillation, or AF, is the most frequent rhythm disorder. It causes the heart to beat irregularly, allowing blood to pool and form clots that can lead to a stroke. Only 30 of those 264 patients, 11.4 per cent, actually had a condition requiring medical intervention.

The electrocardiogram function built into smartwatches has hard limits. Machines found in GP surgeries and hospitals capture 12 different electrical measurements, offering doctors a detailed view. Most ECGs in watches are "single lead," relying on just one electrode sensor to gauge the heart's electrical activity, says Ruth Goss, a cardiac nurse at the British Heart Foundation.

Harmless extra beats, exercise, movement, or poor skin contact can all trigger false alarms. Smartwatches aren't built to give you a diagnosis.

Repeated alerts are driving users toward anxiety and more doctor visits. A 2024 study in the Journal of the American Heart Association involved 172 people with AF. One in five using a smartwatch or fitness tracker said they felt intense fear when warned of a possible episode. These wearers reported no more symptoms than non-wearers, yet over nine months they had 50 per cent more appointments, heart tests, and procedures related to AF.

AF patients who used the devices showed higher cardiac-specific anxiety. Twenty per cent described being triggered by device alerts into intense worry, says Lindsey Rosman, an assistant professor of medicine at the University of North Carolina School of Medicine who led the research. She told Good Health about these findings.

Nearly half of wearable users checked their heart rate or ran an ECG every day, often out of habit rather than because they felt sick. Routine checking tends to feed anxiety instead of calming it. Most people lack the context needed to understand and respond to health alerts. If you do not know your normal heart rate, any unusual reading feels like a red flag. A faster pulse after climbing stairs is nothing to worry about. Without that context, an alert can feel like an emergency.

Doubts also surround "stress" scores offered by many smartwatches. In a 2025 study in the Journal of Psychopathology and Clinical Science, 781 students wore a Garmin watch for three months. The device tracks changes in the time between heartbeats to see how the body responds to pressure or exertion, then calculates a stress score based on that data.

Bjorn Siepe from Philipps University of Marburg in Germany led an investigation that put smartwatch stress data side by side with student self-reports collected multiple times daily. The results showed a consistent mismatch between what the device claimed and how students actually felt at that moment. 'What users reported about their stress level and what the watch reported consistently failed to line up,' Siepe states plainly.

The problem becomes obvious during movement. When a person dances or walks fast, the smartwatch often interprets this physical exertion as high stress instead of normal activity. Seeing those numbers flash on a screen can make someone worry they are failing at life tasks even though there is no logical reason for such concern. Ruth Goss warns that while these gadgets help track exercise and health patterns over time, they lack the precision of medical tests found in GP surgeries or hospitals. Devices like an ECG or a cuff-based blood pressure monitor remain far more reliable for actual diagnosis.

It takes very little effort for people to become obsessed with fluctuating numbers on their wrist. For some individuals, wearing a fitness tracker damages their mental wellbeing more than simply leaving it at home. The public needs to understand that these screens offer only limited access to the truth about their internal state. Government regulations or health directives often push consumers toward trusting consumer electronics over professional medical advice without explaining this gap clearly enough.