If you’re looking to track your blood pressure on your own, nowadays you’re spoiled for choice. There are wearable watches and rings from brands like Apple and Oura, plus traditional inflatable cuffs that can be used at home.
But a new competitor is now entering the fray, claiming to do something nobody else has done yet. Signal has launched a ring to measure blood pressure without ever using a traditional cuff to calibrate the device.
And it doesn’t require a membership — a tempting perk when Oura, the leader in smart rings, asks for a monthly or annual fee from users to fully access their health metrics.
Why is it a big deal to go cuffless, and will the new $399 ring be accurate?
Tracking a ‘silent killer’
Staying on top of blood pressure is important. That’s because when it stays high — something nearly half of Americans deal with — it can be a “silent killer.”
Over time, high blood pressure can damage vessels and strain the heart, leading to heart attacks, stroke, or kidney failure.
Tracking can help identify a problem early. And if you’re already diagnosed with high blood pressure, aka hypertension, it can help you stay on top of it by making sure meds and lifestyle changes are making a difference.
Unfortunately, it’s a hard measurement to get. Even at the doctor’s office, experts estimate 20-45% of cases are improperly diagnosed because of bad blood pressure measurements.
Everything from when you last ate to whether you smoked or had coffee that day, if your legs are crossed, or if a cuff is too small or large, can cause an inaccurate blood pressure reading.
And these are using the optimal machinery — upper-arm inflatable cuffs you’re familiar with at the doctor’s office. These inflate to detect subtle vibrations in the artery, converting measurements of those vibrations into an estimate of blood pressure.
Wary of wearables
Wearables offer a very convenient alternative that doesn’t require the bulky machinery. It also has the advantage of constantly taking readings, which is important when blood pressure varies considerably throughout the day.
But doctors have always been extremely skeptical about their use. Last year, researchers published a paper arguing that because the way wearables measure blood pressure is so different from the established cuff devices, no one knows if they’re actually accurate.
Most wearables get around this by asking users to get a cuff measurement so the watch or ring has a baseline, and routinely update the system with cuff-derived data so it can be calibrated.
In short, even “cuffless” devices still rely on a cuff.
There are also other issues, like arm position and skin color, which can throw off the sensors on wearables, making readings inaccurate.
Oura doesn’t even directly measure blood pressure, they specify it’s “blood pressure signals,” tracking changes over time.
Going cuffless
Signal says their new watch, which is available for pre-order, doesn’t need a cuff — ever. Not for a baseline, and not for a calibration.
They say the ring has a faster sensor that measures specifically blood pressure by assessing the “shape and timing of the pulse.” The ring will measure in real-time throughout the day, but also offers “Zen-mode” a guided reading for reassurance.
“It reads blood flow at far higher resolution than earlier devices, which exposes detail in the pulse wave that was invisible before. Those finer features carry the fingerprint of vascular tone that everyone else misses,” the company said, adding that their ring reads blood flow 4-5 times faster than other trackers.
Doctors recommend those concerned about blood pressure to talk to an expert before buying a new device.
“Patients should talk to their doctor about whether and how to monitor their blood pressure,” Dr. Lindsey Rosman, a cardiologist, told CNET. “And how any device fits into their overall hypertension management plan, rather than adopting new tools on their own.”
