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Dr. Alessandro Giardini
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It is an increasingly common reason families contact me. A parent notices their child's Apple Watch, Garmin, or Fitbit has flagged something: a heart rate of 180 beats per minute during sleep, an alert about an irregular rhythm, or a notification that an ECG recording looked unusual. The device sounds certain. The parent, understandably, is alarmed. What these alerts actually mean, and what they do not mean, is something every family dealing with this situation needs to understand clearly.
Modern consumer smartwatches measure heart rate continuously using optical sensors on the wrist. Most use a technique called photoplethysmography, which detects blood flow changes through the skin with a light source. This is useful for tracking trends but is not the same as a medical-grade electrocardiogram.
Some devices, including certain Apple Watch models, can generate a single-lead ECG recording when the user places a finger on the digital crown. That is genuinely useful clinical information, and a 2023 study from Stanford Medicine found that smartwatch recordings helped detect arrhythmias in paediatric cardiology patients. The devices can pick up real signals. Interpretation, however, is where the difficulty lies.
Consumer smartwatch algorithms were developed and validated in adults. Children have faster baseline heart rates, different ECG characteristics, and rhythm variations that are entirely normal in younger people but that adult algorithms may flag as abnormal. A child sleeping at a heart rate of 100 beats per minute is not unusual. An algorithm calibrated for a 45-year-old may classify that as tachycardia. Similarly, sinus arrhythmia, a completely normal variation in heart rate with breathing that is common in children and teenagers, can generate irregular rhythm alerts.
A 2025 scoping review published in Translational Pediatrics concluded that smartwatches in children represent a mixed blessing, with potential benefits alongside real risks of triggering unnecessary anxiety and inappropriate clinical investigations.
There is a well-recognised cycle that smartwatches can create in families. The device flags something. A parent becomes anxious. Their child notices the parental worry, or sees the alert themselves. Anxiety rises in the child as well. Heart rate follows. When the device reads a genuinely elevated rate and flags it again, the cycle tightens.
This is not hypothetical. It happens regularly. I see teenagers who have developed significant health anxiety rooted in a single smartwatch notification, spending hours each day checking their wrist data and interpreting every elevated reading as evidence of a problem.
Smartwatch data is best used as a prompt for professional review, not as a diagnostic tool in its own right.
Not every alert requires a cardiology appointment. Many can be understood and contextualised without specialist input.
A slight increase in the heart rate during sleep, in an otherwise well child with no symptoms, is usually benign. Movement artefact, fever, a restless night, or a device fitting loosely on the wrist can all produce misleadingly high readings.
Some alerts do warrant proper assessment. An episode the child also felt, accompanied by dizziness, near-fainting, an unusually fast heart rate that started and stopped abruptly, or breathlessness at rest deserves evaluation. An alert that coincides with actual symptoms is clinically more meaningful than a silent background reading the child was unaware of. As a paediatric cardiologist, I make that distinction in every consultation where a family brings in watch data: what did the child feel, and when?
Family history matters here as it does everywhere in paediatric cardiology. Relevant concerns, including unexplained sudden death, inherited arrhythmia syndromes, and hypertrophic cardiomyopathy, raise the threshold for investigation. I take those histories seriously.
When a family brings smartwatch readings to a consultation, I treat the data as a starting point rather than a conclusion. The history of what the child felt during flagged episodes, exercise tolerance, any associated symptoms, and family background all inform the picture far more than a heart rate graph.
A standard 12-lead ECG provides considerably more diagnostic information than a single-lead smartwatch recording. Intermittent rhythm problems may not appear on a brief ECG, which is where ambulatory monitoring over 24 to 48 hours, or longer with a patch monitor, becomes useful. The smartwatch alert, in those cases, is a useful clue that something needs capturing properly, not a diagnosis.
In the majority of families I see in this situation, the assessment is reassuring. Explaining what the device was likely detecting, what a normal ECG and echocardiogram show, and when to act on future alerts gives families a framework that reduces anxiety considerably.
Not necessarily. Movement during sleep, fever, a loose-fitting device, and position changes can all produce elevated readings. If the child was well and did not feel anything, the reading is most likely an artifact. A single reading in isolation is rarely clinically significant.
Can a smartwatch ECG diagnose SVT in a child?
A smartwatch single-lead ECG can sometimes capture a fast rhythm, which is useful information. It cannot reliably distinguish SVT from other causes without proper clinical review. Specialist assessment with a 12-lead ECG provides a much more complete picture.
Should I take my child to A&E because of a smartwatch alert?
Only if your child currently feels unwell, is experiencing dizziness, near-fainting, breathing difficulty, or the heart is still racing and they feel it. A smartwatch alert without active symptoms is rarely an emergency, but it is worth arranging a paediatric cardiology review if you are concerned.
How reliable are smartwatch heart rate monitors in children?
Less reliable than in adults. Algorithms and sensors were developed for adult physiology. Children's faster baseline rates and different ECG characteristics mean alerts are more likely to be false positives. That does not mean all alerts can be dismissed, but context and symptoms matter far more than the alert alone.
Can I bring smartwatch data to a cardiology appointment?
Yes, and it is often helpful. Screenshots of flagged readings, timestamps, and notes about what the child felt during those episodes all assist the assessment. The data informs the history; it does not replace the clinical evaluation.
Author: Dr. Alessandro Giardini, MD, PhD
Written 22/05/2026