Signal smart ring claims cuffless, calibration-free blood pressure readings

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Blood pressure has long been considered the "holy grail" of PPG-powered wearable tech. Because (up until now) you really need an inflatable cuff to measure, or at least to calibrate, blood pressure readings, and that's been difficult to do with a smartwatch alone.

The Huawei Watch D series incorporated a cuff into the smartwatch itself, while Apple has introduced its Hypertension Detection feature, which earmarks possible hypertension after 30 days of using an Apple Watch , but doesn't actually provide blood pressure readings. No LED-based device has really been able to crack it. Until now, apparently.

The Signal Ring is the brainchild of Tom Moss, an ex-head of Android at Google who's founded several companies since leaving Google and co-founded several other companies, including drone business Skydio, which eventually ended up being bought by Razr.

Signal is a smart ring with a difference: rather than provide lots of different metrics such as the Oura Ring 5 or the Samsung Galaxy Ring , or use AI assistants like the Google Fitbit Air, it's designed by "a very smart group of multidisciplined people focused on a single problem" — and that problem is blood pressure, which Moss was inspired to tackle after a cardiac event, a 'hypertensive emergency',

"My blood pressure was 250. If you can imagine, for blood pressure, 120 [over 80] is healthy and fine," Moss told me. "So 250 is just like an insane amount of pressure."

After his event, Moss attempted to track his blood pressure, but had difficulty with incorrectly-sized cuffs and sought a more technical solution. "I went online, I bought every kind of device that told me it could track my blood pressure, wearable or otherwise, and they're all garbage."

(Image credit: Signal) Some watches, such as the Samsung Galaxy Watch series, use an initial blood pressure cuff reading to calibrate, then estimate your blood pressure by looking at other vital signs in between calibrations. But Moss found this approach frustrating and inaccurate. "We needed a way to measure blood pressure from a wearable, not just measure changes from a baseline."

Working with scientists and engineers from Masimo ( the company that sued Apple over infringement of LED-based heart rate sensing technology ) Moss developed the Signal Ring over three years, which can take on-the-spot blood pressure readings and use a single number — a metric called 'mean arterial pressure' — to passively track blood pressure throughout the day, broadcasting the information to its companion app over Bluetooth like any other wearable.

(Image credit: Bokeh Stock / Shutterstock) I asked him how a startup could do something that Apple, Oura, Samsung, Google, and others had failed to do, and his response was one of specialism.

"This is our sole focus as a company," said Moss. "My co-founders have decades of knowledge on PPG, state-of-the-art processing... we have a very smart group of multidisciplinary people focused on a single problem."

Without needing to cram in sensors required for other features, such as accelerometers for counting steps, the team was reportedly able to crack the blood pressure mystery. "It's not AI or anything, it's not that we use some sort of new, magic technology. We put the best people, the most equipped, to work on it."

Exciting stuff in the wearables space, but only real testing will confirm its accuracy compared to conventional blood pressure measurements. Pre-orders for the Signal Ring are available now, priced at $399 (around £295 / AU$770) with no subscription (thank goodness!) and are likely to ship in October.