Huawei made a blood pressure cuff fit into a smartwatch, and I’m obsessed with the engineering

What once started as a health companion and second screen on your wrist has turned into something a lot more useful. Over the years, smartwatches have become more advanced, and their health tracking features are even more accurate and varied. After reviewing wearables for years, I got good at guessing the experience with new smartwatches.

But Huawei managed to have me obsessed with one of its latest models–and it’s the strap that has my attention. Packed on the underside of the strap is a thin inflatable bladder that runs along the inside of the band. Start a blood-pressure measurement, and that bladder begins expanding against your wrist, tightening in a way that’s familiar to how a doctor wraps a cuff around your upper arm.

This might make the Huawei Watch D3 sound like a thick and heavy wearable tech. But in reality, the Watch D3 is only 11.3mm thick, weighs just over 70 grams with its strap, and has a 1.92-inch AMOLED display. Huawei has also narrowed the inflatable section and made the strap 7.5 grams lighter than before. The blood-pressure feature is fascinating, as the company isn’t making it a software feature.

How does a blood pressure cuff fit inside a watch?

The trick starts with what Huawei calls its 2-in-1 strap-airbag. Rather than having a normal watch band sitting flush against your skin, part of the D3’s strap contains a thin mechanical airbag. When a measurement begins, the watch pumps air into that chamber, causing it to expand inward and apply pressure around your wrist.

Huawei uses the oscillometric method, the same broad measurement principle used by many electronic blood-pressure cuffs. A high-precision pressure sensor works alongside Huawei’s TruSense system to detect the pressure changes created by your pulse while the airbag is inflated. From those changes, the system calculates systolic and diastolic blood pressure.

Again, this is a proper mechanism that doesn’t rely purely on an optical sensor and an algorithm to infer your blood pressure. You can see it in the photos I took. The strap may look unusually thick, but that’s only because it was inflated to take a BP reading. Put the watch on, and that extra material pretty much disappears. You don’t particularly feel it out of place compared to your usual strap. Once you start the measurement, you can physically feel the pressure build as the bladder expands.

Even taking the reading has a very specific posture

To make things as accurate as possible, Huawei gives you some tips for the best possible results, and it starts with your posture. Your watch arm should be steady, elbow bent with your palm facing your chest, while the wrist and palm remain relaxed. It also needs you to support that elbow with your other hand so the Watch D3 sits roughly level with your heart.

Your feet should be flat on the floor and uncrossed, and you’re supposed to remain quiet and avoid moving your fingers, arm, or body while the cuff is working. I was explaining the watch to a friend when taking a measurement, and the Watch D3 promptly told me to pipe down. You can see the posture in the images I’ve shared.

The watch is trying to recreate, on your wrist, the controlled conditions that make a conventional cuff useful. Huawei even asks users to enter their wrist circumference so the watch can match the correct airbag size, with separate M and L strap-airbags supplied for wrists between 130mm and 210mm. So there’s a lot more thought put into this to avoid any kind of misreading. Health is a pretty serious matter for many, so avoiding any false results is key here.

Huawei is doing something very different from Apple and Samsung

Apple’s current Watch implementation looks for patterns associated with hypertension using its optical heart sensor over a 30-day evaluation period. It does not give you an on-demand systolic and diastolic measurement. If the Watch flags possible hypertension, Apple specifically recommends using a third-party cuff for seven days and discussing the results with a healthcare professional.

Samsung goes further. Compatible Galaxy Watches can produce blood-pressure values, but the system first needs to be calibrated against an upper-arm cuff, including three measurements during initial calibration, and Samsung requires recalibration every 28 days. Huawei’s solution, on the other hand, is mechanical by comparison. Sure, the Watch D3 is slightly bulkier and more specialized than a conventional smartwatch, but I find the engineering much more interesting.

It takes it one step further

The Huawei Watch D3’s strap also enables another cool feature, which is ambulatory blood pressure monitoring, or ABPM. You can start a 24-hour monitoring plan and have the watch take readings at preset intervals throughout the day and night. Huawei’s default schedule can prompt daytime measurements every 30 minutes. At night, the Watch D3 can automatically inflate while you’re asleep without requiring you to assume the daytime measurement posture.

Once the monitoring period ends, Huawei Health can show daytime, nighttime, and 24-hour averages and generate an ABPM report that can be saved or printed. Of course, the trade-off here is battery life. Huawei rates the watch for up to six days in typical use, while continuous ABPM cuts that estimate to about one day.

The Watch D3 is still a smartwatch, but it’s also certified

The engineering on the Watch D3 is quite intriguing. Its mechanical moving parts are things that set it apart. Still, it doesn’t look like dedicated medical equipment. On the outside, it has that familiar shape of a smartwatch. The white strap unit I have looks elegant and sleek. Its 1.92-inch display dominates the front. All of the UI and other elements function exactly as you’d expect them to.

It might not look like it, though this is kind of impressive when you read the marketing material. Huawei advertises the Watch D3 as a medical-grade wrist blood-pressure monitor in supported markets, and the UK product page says it is CE-MDR certified. However, measurement availability and regulatory status vary by country. It is worth noting that the measurements should only be treated as guidance. Any unusual results should be properly discussed with an actual healthcare professional. The main advice is not to self-diagnose from a single smartwatch reading.