A smart ring developed by Sky Labs measured blood pressure with mean differences of less than 1 mmHg compared to a standard arm-cuff sphygmomanometer in a first-in-human clinical study, matching the accuracy threshold that regulators and clinicians have long treated as the gold standard. The finding, published in the Journal of Korean Medical Science, lands at a moment when the FDA has issued draft guidance spelling out exactly how cuffless blood pressure devices must prove themselves before reaching consumers. Whether that lab-tested precision holds up during the messy reality of daily life is the question that will determine if rings can actually replace cuffs for the tens of millions of people managing hypertension.
Why ring-based blood pressure tracking matters right now
High blood pressure is the single largest modifiable risk factor for cardiovascular death, yet most people check it only during occasional clinic visits. A device worn continuously on a finger could, in theory, catch dangerous spikes between appointments and document how blood pressure responds to sleep, stress, and medication timing. The CART-I plus ring from Sky Labs is the first ring-form-factor device to produce mean differences below 1 mmHg for both systolic and diastolic readings against a reference auscultatory sphygmomanometer in a controlled clinical setting. That level of agreement meets the tightest accuracy benchmarks used in traditional cuff validation studies and suggests that, at least in the lab, a ring can perform like a clinic-grade cuff.
The catch is that the study tested participants seated and at rest, the same controlled posture used to validate conventional arm cuffs. A reasonable expectation, grounded in the physics of pulse-wave sensing and the known behavior of optical blood pressure estimation, is that ring accuracy will hold under those seated, rested conditions but drift beyond 5 mmHg from arm-cuff readings during routine daily activity once the initial calibration window expires. That hypothesis is testable with paired home readings over 14 days, but no publicly available dataset from Sky Labs or any independent group has yet reported those results. Until someone runs that experiment and publishes the data, the clinical promise of cuffless rings remains tethered to a narrow set of lab conditions rather than the full variability of everyday life.
Clinical trial data and FDA standards shaping the threshold
The first-in-human study compared the CART-I plus ring against a trained observer using an auscultatory sphygmomanometer, the same reference method the FDA specifies in its draft guidance on cuffless device evaluation. The study reported mean differences of less than 1 mmHg for both systolic and diastolic blood pressure, a result that falls well within the accuracy corridor traditionally required for arm-cuff clearance. The narrow standard deviation of the differences, along with the absence of systematic bias across the tested pressure range, strengthens the case that the ring can reliably mirror cuff readings under the specific conditions studied.
Separately, a validation study registered on ClinicalTrials.gov under identifier NCT06513975 is testing the CART BP wearable cuffless monitor against a dual-head stethoscope auscultatory method. That trial’s results have not yet been posted publicly, so its contribution to the evidence base is limited to confirming that a broader validation effort is underway with the same comparator method used in the original study. The registration details indicate an intent to evaluate performance across multiple blood pressure ranges, which will be important for understanding whether the ring maintains accuracy in people with more severe hypertension or lower baseline pressures.
On the regulatory side, the FDA has formally recognized the IEEE 1708 standard, including its Amendment 1, as the benchmark for wearable cuffless blood pressure devices. That recognition gives device makers a defined technical target for metrics such as bias, precision, and test protocols, but the FDA’s database entry also notes specific clause conflicts and considerations, signaling that meeting the standard on paper does not automatically translate into regulatory clearance. Manufacturers still need to satisfy the clinical evidence expectations laid out in the agency’s draft guidance, which specifies acceptable study designs, comparator methods, and analytical frameworks, including how to handle repeated measures and how to demonstrate performance across diverse patient groups.
Taken together, the published ring study, the ongoing trial, and the regulatory framework sketch a clear threshold: to move from novelty to clinical tool, a cuffless ring must show arm-cuff-level accuracy in controlled conditions, maintain that performance over time, and do so in a population that reflects the real-world mix of age, comorbidities, and skin tones. Sky Labs has cleared the first of those hurdles in a relatively small, controlled cohort; the remaining hurdles will determine whether payers and clinicians treat the device as more than a wellness gadget.
Calibration drift and the gap between lab and life
Expert analysis published in a peer-reviewed assessment of cuffless blood pressure limitations identifies calibration as the central vulnerability of wearable devices. Optical and pulse-wave-based sensors require periodic recalibration against a reference device, and the interval at which that calibration degrades varies by individual physiology, ring fit, skin perfusion, and ambient temperature. The study’s sub-1-mmHg accuracy was measured shortly after calibration under controlled conditions. No publicly released primary data show how that accuracy changes over days or weeks of continuous wear without recalibration, leaving open the possibility that a ring could appear flawless in the lab yet drift into clinically misleading territory in home use.
Body position adds another variable. Standing, walking, and even crossing legs alter hydrostatic pressure in the finger relative to the heart. Traditional arm cuffs account for this by standardizing the measurement posture and arm position, but a ring worn throughout the day cannot enforce that discipline. The expert literature flags this mismatch as a likely source of divergence between ring readings and cuff readings during normal activity, though quantified ambulatory data from the CART-I plus ring have not been published. Without those data, it is difficult to know whether algorithms can fully compensate for posture and movement or whether users will need explicit prompts to pause and sit before each clinically meaningful measurement.
There is also the question of population diversity. The first-in-human study provides summary statistics but has not released patient-level data or subgroup analyses by age, skin tone, body mass index, or comorbidity. Because optical signals interact differently with melanin, tissue thickness, and vascular stiffness, a ring that performs well in a relatively homogeneous sample might show larger errors in people with darker skin, peripheral vascular disease, or advanced diabetes. Regulators will likely expect future trials to stratify performance across such subgroups and to demonstrate that calibration procedures do not systematically disadvantage any one demographic.
For now, the evidence supports a cautious but optimistic interpretation. Under ideal conditions, a smart ring can match the accuracy of a clinic-grade cuff, satisfying both traditional validation benchmarks and the emerging FDA framework for cuffless devices. The unanswered questions center on durability of calibration, robustness to movement and posture, and equity of performance across diverse users. As additional trial results emerge and manufacturers publish long-term, real-world datasets, clinicians and patients will be better positioned to decide whether finger-worn sensors can shoulder some of the burden currently carried by arm cuffs in the management of hypertension.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
