Circular Ring 2 Can Now Measure Your Blood Pressure, No Cuff Required
Smart ring maker Circular has launched blood pressure monitoring for the Circular Ring 2, allowing users to estimate both systolic and diastolic blood pressure directly from a finger in roughly 60 seconds. The feature is now live in the Circular app at no additional cost and requires no subscription.
The Science Behind Cuffless Blood Pressure
Traditional blood pressure monitoring works by squeezing an artery with an inflatable cuff, closing it off completely before slowly releasing pressure and listening for the moment blood flow resumes. A ring obviously can’t do that. Instead, Circular Ring 2 relies on a technique called Pulse Wave Transit Time, or PWTT, which measures how quickly the pulse wave generated by each heartbeat travels from the heart to the finger.
Every heartbeat produces two distinct, measurable signals. The first is an electrical pulse, visible as the R peak on an ECG trace, marking the exact moment the heart contracts. The second is a mechanical pulse wave that follows a fraction of a second later, altering how much light the skin absorbs, a signal known as PPG, or photoplethysmography. By timing the gap between these two signals, the ring can calculate how fast the pulse wave is travelling.
That timing matters because pulse waves move faster when arteries are stiffer and under greater pressure, and slower when pressure is lower. This relationship between wave speed and blood pressure is well established in cuffless monitoring research. Most wearables only capture PPG, which shows the wave itself but offers no fixed electrical starting point to time it from. Circular Ring 2 is built to capture both ECG and PPG simultaneously, which is what makes calculating transit time from a single finger possible.
Why the Ring Still Needs a Cuff to Calibrate
While transit time reveals how fast a pulse wave is moving, it can’t independently translate that speed into an actual blood pressure reading in millimetres of mercury. The relationship between wave speed and blood pressure depends on individual factors like arterial stiffness, vessel geometry, and finger anatomy, none of which can be determined from the signal alone.
To solve this, users first take three blood pressure readings using a standard cuff monitor and enter the results into the Circular app. Those three readings establish a personal baseline connecting an individual’s transit time data to real blood pressure values. Once that calibration is complete, ongoing monitoring can be done entirely through the ring, without needing a cuff for each reading. Circular recommends recalibrating with a cuff every 30 days, since arterial properties naturally shift over time due to factors like age, weight, medication, and season.
How a Reading Actually Works
Taking a measurement requires completing an electrical circuit across the body, something the ring can’t do on its own. To do this, users rest a finger from their opposite hand lightly on top of the ring, allowing current to travel up one arm, across the chest, and down the other. Notably, light contact is important. Pressing too firmly can compress the tissue beneath the sensor and introduce noise into the PPG portion of the reading.
Rather than relying on a single heartbeat, the ring waits for 20 consecutive high-quality beats before returning a result. A single beat’s transit time is a noisy data point on its own, easily thrown off by small hand movements, changes in ambient light, or shifts in contact pressure. Instead of smoothing over that noise, Circular’s algorithm simply discards any beat that doesn’t meet its quality threshold, meaning a full session typically takes around 60 seconds, but can take longer if the user’s hand moves during measurement.
>> See our review of the Circular Ring Slim
Getting an Accurate Reading
Because factors like caffeine, exercise, posture, and even recent food or alcohol intake can meaningfully shift blood pressure, the calibration process walks users through a short checklist based on guidance from the European Society of Hypertension. This includes confirming they’ve avoided caffeine, alcohol, exercise, food, and smoking in the 30 minutes prior, sitting quietly for five minutes beforehand, and maintaining supported posture with both feet flat on the floor during the reading.
Understanding the Results
Each measurement returns a systolic and diastolic estimate alongside heart rate, timestamped and classified into one of six bands aligned with European Society of Hypertension categories: Optimal, Normal, Elevated, and Hypertension stages 1 through 3. The free version of the feature includes unlimited measurements, a daily average view, a full log of that day’s sessions, a running breakdown of how historical results fall across the different bands, and a contextual health tip attached to each result.
What’s Coming Next
Circular has confirmed that more advanced blood pressure insights are already in development, including longer-term trend analysis, time spent within a target range, and a shareable PDF summary designed for doctors. These additional features will eventually sit behind a premium tier, unlocked either through the company’s in-app currency or a direct payment, though the core blood pressure measurement itself will remain free. Circular also plans to feed blood pressure data into its AI coaching assistant, Kira, allowing it to factor pressure trends into broader recommendations alongside sleep, recovery, and activity data.
Not a Medical Device
Circular has been explicit that the Ring 2 remains a wellness device rather than a certified medical one. The blood pressure values it produces are intended for tracking trends over time, not for diagnosing conditions or guiding treatment decisions such as adjusting medication. Anyone seeing consistently elevated or high readings is advised to consult a healthcare professional and confirm results using a clinically validated cuff rather than acting on the ring’s data alone.
The update arrives as blood pressure tracking becomes an increasingly sought-after feature in the wearables space, an area many smart rings and watches have struggled to address given the physical constraints of cuffless measurement. By combining ECG and PPG sensing in a single ring-based device, Circular is positioning blood pressure monitoring as a meaningful step toward more comprehensive, continuous cardiovascular tracking outside the clinic.
Keen tech writer outside of my day job in I.T. and spending time with my family.
