People wearing an Apple Watch, Galaxy Watch or Fitbit often ask how much to trust it. The short answer: the ECG and some alerts — irregular rhythm, sleep apnea and hypertension — passed regulators as medical software; blood oxygen, calories and steps are wellness data. None replaces a diagnosis, and any warning or symptom belongs with a doctor.
- Clearance covers software: regulators review a named programme and its stated use, not the watch.
- Wrist ECG: one lead, 30 seconds, aimed at atrial fibrillation.
- Apnea and hypertension alerts screen: they flag patterns, seek testing and miss cases.
- Wellness data: oxygen, pulse and calories are not diagnostic.
The approval paradox
In September 2025 the US FDA cleared Apple’s hypertension notification through 510(k). Yet the Apple Watch manual, on the same page, says:
“Tu Apple Watch no es un dispositivo médico”.
Both are true. Clearance covers a named software function and the maker’s stated use, not the whole watch. FDA filings describe the ECG app and hypertension alert in these terms:
“software de electrocardiógrafo para uso sin receta”
“software de notificación basado en aprendizaje automático”
The programme and its claim are authorised, not the hardware.
Europe’s Regulation (EU) 2017/745 includes “programa informático” intended by the maker for diagnosis, prevention, monitoring or prediction of disease. “Destinado” is key: a step counter is not sold for that purpose.
FDA records list Apple’s ECG app and irregular-rhythm alert as De Novo on 11/09/2018; Fitbit’s ECG app by 510(k) on 11/09/2020; Apple’s sleep-apnea alert by 510(k) on 13/09/2024; and Apple’s hypertension alert by 510(k) on 11/09/2025. Samsung said its Health Monitor (ECG and blood pressure) won CE marking in December 2020, reaching 28 European countries, Spain included. Apple announced on 27 March 2019 that its ECG app and irregular-rhythm notifications had CE marking in the EEA; a free watchOS 5.2 update brought them to 19 European countries, Spain included.
What the ECG can and cannot do
The wrist ECG is the most mature feature and targets atrial fibrillation. Apple says it runs on Series 4 or later and all Ultra models, records for 30 seconds with a finger on the Digital Crown, and is not intended for under-22s. The trace resembles lead I; a clinical ECG uses 12 leads, or 12 angles. Apple concedes that one lead can assess rate, rhythm and AF, adding:
“no sirven para identificar otras afecciones, como los infartos de miocardio”.
It cannot detect heart attacks, clots, stroke, hypertension, heart failure, high cholesterol or other arrhythmias. Version 1 screened AF at 50–120 beats per minute; version 2 at 50–150; outside those ranges results may be inconclusive. A “ritmo sinusal” result covers only 30 seconds and does not prove the heart stays regular or that health is good. Export the PDF from the Salud app for a cardiologist.
Screening versus wellness
Apnea and hypertension notifications are screening tools that flag a pattern, not diagnose; both admit missed cases. Apnea uses the accelerometer to count overnight breathing disturbances. It needs a Series 9 or later, Ultra 2 or later or SE 3, at least 10 nights of wear in 30 days, and is designed for over-18s without a prior diagnosis. Apple says:
“no se ha diseñado para diagnosticar, tratar o ayudar a gestionar la apnea del sueño”
“no todas las personas con apnea del sueño reciben notificaciones”.
Hypertension alerts ask for upper-arm cuff readings twice daily for seven days and medical advice if a pattern appears. They are not advised for people already diagnosed, under-22s or during pregnancy, and Apple warns it cannot identify “cada caso”. The watch is a fair early alarm and a poor tranquilliser: no alert does not prove health; an alert means get measured properly.
Blood oxygen, on Series 6 or later and all Ultra, carries this warning:
“no están pensadas para uso médico”
Most people read 95–100 percent and a sleep dip is normal. Heart rate uses green LEDs and photodiodes to sense wrist blood flow; Apple’s optical sensor supports 30–210 beats per minute and data may include “anormalmente altas o bajas” readings. Calories are the weakest area: a 2020 systematic review in JMIR mHealth and uHealth examined 158 publications across nine brands. Steps are wellness too.
The boundary between regulated and wellness runs feature by feature, not by the box. A smartwatch helps when it prompts a check or catches an irregular rhythm, but a normal number should never talk anyone out of care. Neither clearance nor a reading is a diagnosis.