While millions suffer under a virus that hits the respiratory system, Apple has launched a new watch that may be able to detect respiratory problems with an oxygen sensor. We tried out the new Series 6 and its cheaper Watch SE counterpart to see how useful the new features are.

You can hardly tell the difference between newer models of the Apple Watch at first glance. The familiar old rounded square of black with a single crown has changed little in recent years.

But pretty soon the differences between the new Apple Watch Series 6, the new entry-level model SE and the predecessor Series 5 become apparent.

While the display of the cheaper Apple Watch SE switches off to save power, the screen of the Series 5 and 6 remains on all the time - albeit slightly less brightly.

If you take a closer look, you will also notice a difference between the two watches with always-on displays. Apple says that the Series 6 has a two and a half times brighter screen in passive mode than the previous model.

While you will indeed notice this in practice, it probably won't feel 250% as bright.

Take any of these watches off and look at the back and you'll see another difference. New sensors and four LED clusters enable the Series 6 to detect how much oxygen is being carried in your red blood cells for an oxygen saturation (SpO2) reading.

Oxygen levels at a glance

Arriving in the middle of a pandemic caused by a virus that attacks the respiratory system, this sensor is easily the most promising health feature on a smartwatch since the introduction of sensors to check for heart rhythm problems.

Apple believes this function will also play a role in detecting chronic lung diseases, asthma and sleep apnea, as well as the lung disease Covid-19. Athletes who monitor their vital signs during workouts will likely also want to keep an eye on this data.

If you go to a hospital, doctors will likely be measuring your SpO2 value with a conventional pulse oximeter on your fingertip or earlobe.

On the new Apple Watch, however, it will be measured on your wrist, just like on smartwatches from other manufacturers who have adopted this sensor. The LED lights shine into the skin, the sensors register the colour of the blood and use this to tell your SpO2 value.

The method uses the fact that blood shows different colours depending on its condition: Saturated, oxygen-loaded haemoglobin is bright red and absorbs red light in particular. Unsaturated haemoglobin appears dark red to bluish and absorbs mainly light in the infrared range. In practical tests, the Apple Watch 6 delivers virtually identical values as a special pulse oximeter on the fingertip.

Not a medical device

With SpO2 values between 93% and 100%, everything is fine, say doctors. If lower values persistantly appear, you should seek medical advice.

Despite its hopes in detecting respiratory problems and diseases, Apple is marketing the function strictly as a fitness feature and says users should not rely on this alone to get a sense of the respiratory health.

This also has to do with the fact that the watch would fall under much stricter legal conditions if Apple declared the watch a medical device.

Doctors also say that good SpO2 values can't be taken as a clean bill of health, and that some patients infected with the novel coronavirus and showing symptoms will still have healthy oxygen levels.

In contrast to the single-channel ECG, which was introduced with the Apple Watch 4, you do not necessarily have to start a separate app to measure blood oxygen, but can have the values recorded in the background, for example at night for sleep analysis.

Also new in the Apple Watch Series 6 is another altimeter, which now runs constantly in the background during normal operation and is much more precise than in the older models.

This is not only useful for rock climbers and mountain bikers, but also to give more precise readings on things like jogging uphill or climbing stairs.

No big performance leap

Apple says it's made improvements with the main S6 processor, which is supposed to be 20% faster. In everyday use, however, there is no noticeable difference in performance compared to the Series 5 - although Siri perhaps responds a tiny bit faster.

The new chip is also said to be more efficient with battery usage. And yet even here, Apple's marketing doesn't quite live up to the expectations it has made.

While performance is smooth, we can expect the new processor to be properly tested in a year or two when WatchOS 9 or 10 arrives with more demanding features.

 - dpa