The Apple Watch now has another feature registered as a medical device, with Apple rolling out its TGA-approved hypertension detection update to Australians this week.

The Hypertension Notifications Feature is a class IIa medical device (meaning low to moderate risk) and joins a growing list of smartwatch apps being regulated in the same way as retractors, ultrasound probes and replacement hips.

If wearers turn on the feature, the Apple Watch uses photoplethysmography — a way of measuring blood volume changes through the skin — to analyse cardiovascular data over 30 days.

It then sends the wearer a notification if patterns are consistent with hypertension.