The Circular Ring 2 is an HRV tracker that reads your heart rate variability continuously from your finger. It turns the data into daily recommendations: push or rest. When your HRV drops, the ring tells you what to do about it. Like this: your HRV is 18% below baseline, so move today's session back 24 hours.
Order Circular Ring 2Heart rate variability reflects how your nervous system is coping with stress, training, sleep, illness, and life in general. The problem is that almost every HRV tracker hands you the reading and walks away. You see the number drop, and you have to figure out for yourself whether to train, rest, sleep earlier, or just keep going.
Your HRV dropped 12 points overnight. Most heart rate variability monitors stop there and leave the interpretation to you.
HRV is deeply personal. Comparing your reading to a generic "healthy range" tells you almost nothing about your own recovery.
The actionable layer that turns HRV data into real decisions is usually held behind a monthly fee.
Circular Ring 2 measures your HRV overnight and compares it to your true baseline, not a flat average. Kira reads it against your sleep, stress, and recovery, then writes one clear move for today.
Kira AI reads your HRV against your sleep, stress, and recovery, then writes one specific thing to do today.
Your HRV is tracked across every night, not sampled in 60-second windows during the day.
Run a live HRV measurement from the app whenever you want a spot check.
Your HRV is interpreted alongside your sleep, stress, and recovery, never in isolation. It is read alongside the systems that shape it.
The HRV tracker, the live measurement feature, Kira AI's actionable insights and 14+ core features are all included with your ring, without any subscriptions.
You wake up and your HRV is well below your baseline. Some mornings it is physical. Some mornings it is heavier than that: a difficult week, a low mood, the kind of tiredness that does not come from the gym. Kira AI suggests pushing today's session by 24 hours. You would have probably forced yourself through it otherwise.
Nothing felt off. Work was busy but normal, sleep was around seven hours, no late nights. Then on Wednesday your HRV is the lowest it has been all month. Looking back, the trend has been sliding for four days. The stress was real. You just had not noticed yet.
Two nights of light sleep, and your HRV drops sharper than usual. Kira AI ties it back to the late screen time you logged on Sunday and recommends anchoring your bedtime by 30 minutes tonight. The next morning's reading shows the recovery starting.
You travel across four time zones. Your HRV is fragmented for three days, your sleep is shifted, your temperature is off. Kira AI gives you a specific recovery rhythm that lines up with your body's signals, not the calendar.
You had two glasses of wine with dinner. Your overnight HRV is noticeably lower than the night before. You did not feel it, but your nervous system did. Over time, you start to see the pattern, and it changes how you think about a quiet weeknight drink.
You commit to consistent sleep and steady training for three weeks. Your average HRV climbs across the period. The number itself does not motivate you. What motivates you is seeing the trend respond to choices you actually made.
A long meeting, a flight, a race, a presentation. You run a live HRV reading from the app and get a sense of where your nervous system actually is right now, not where it was last night. The reading helps you decide whether to push hard or pull back.
A heart rate variability monitor that just shows a number is missing the harder half of the job. The number means very little without context. Your HRV always reads against something. Kira AI is built to do that data reading. It watches your HRV alongside every signal Circular Ring 2 captures, finds the pattern, and writes a recommendation in plain language. Push or pull back. Sleep earlier. Skip the second espresso. The answer is shaped to your body and your day, not to a population average.
Circular Ring 2 measures HRV optically, through PPG (photoplethysmography). The sensor reads the blood volume pulse passing through the small arteries in your finger, which is one of the most reliable places on the body for clean optical measurement. The ring sits firmly on the finger with no moving joints under the sensor, which helps the signal stay clean overnight.
Circular Ring 2 uses the RMSSD calculation, which is the most widely accepted method for short-term HRV analysis in scientific literature. The measurement window is a one-minute rolling average.
Overnight continuous measurement is the primary mode, because nighttime HRV is the most reliable window for tracking long-term nervous system health. Live on-demand HRV readings are also available during the day, for users who want a spot check before training, after travel, or during a stressful day.
Circular Ring 2 builds your reference HRV automatically across your first 14 days of overnight wear. This long-term personal average becomes the benchmark for every reading that follows. When your daily HRV is at or above your reference, your nervous system is in a strong position. When it is below, your body is signalling strain.
HRV is a recovery and readiness indicator, not a diagnostic tool. Circular Ring 2 does not diagnose disease, predict illness, detect burnout, or replace clinical evaluation. The ring is not a medical device. For any clinical concern, share your trend data with a doctor.
HRV data is encrypted and processed with GDPR and HIPAA compliance.
Titanium body, hypoallergenic interior
2.55mm thick, 7.8mm wide, 3 grams
Sizes: US 6–14
Battery: 8 days (Power Mode), 5 days (Performance)
Charging: 30 mins via wireless charger
ECG, PPG, temp sensor, 3x accelerometer
Bluetooth Low Energy, Airplane Mode
iOS & Android compatible
GDPR & HIPAA compliant
"I used to see my HRV drop and just kinda ignore it because I had no clue what it actually meant. One morning Kira told me to skip my workout and focus on recovery. I was annoyed lol. Since then I've started paying attention."
"Honestly the biggest thing for me wasn't the HRV number itself. It was seeing how bad sleep and a couple glasses of wine showed up the next morning. You think you're fine until the data calls you out."
"I travel a lot for work and my energy is usually all over the place. The HRV trends helped me realize I was pushing too hard after flights. Kira's recs are simple, but weirdly accurate. Feels like someone looking at the whole picture and telling you what to do."
HRV is one signal in a wider system. Circular Ring 2 reads it together with your sleep stages, recovery, stress, energy, ECG, temperature, blood oxygen, activity load, and Women's Health data. All 14+ features work as one, which is why your HRV stops being a number on a chart and starts being a useful part of your day. That is what makes the recovery decisions actually land.
Tracks breathing rate against your own baseline. Normal resting range: 12–18/min.
Learn when your body is stressed and needs rest or when it is ready to perform.
A 40-second ECG from your finger, with irregular rhythm and AFib detection.
Light, deep and REM sleep mapped across the night, with the timing and quality of each stage.
Shows how much energy you've accumulated based on sleep, stress, recovery, and immune function.
Continuously tracks heart rate with precise PPG measurements via optimal finger placement.
Heart rate variability is the variation in time between successive heartbeats, measured in milliseconds. A healthy heart does not beat at perfectly even intervals. The small variations in those intervals reflect how your autonomic nervous system is balancing rest, recovery, and effort.
Your HRV reflects how prepared your body is for stress and effort. Higher HRV usually points to stronger recovery and a body in a good place to push. Lower HRV often points to strain, poor recovery, or accumulated stress, and is a signal to rest more, sleep earlier, or pull back on training.
The ring measures HRV optically through PPG, by tracking the blood volume pulse through the arteries in your finger. The finger is one of the most reliable places on the body for clean optical HRV measurement, partly because the ring sits firmly without moving across joints.
Circular Ring 2 uses RMSSD, the most widely accepted short-term HRV measurement in scientific literature. The measurement window is a one-minute rolling average.
Overnight continuous measurement is the main mode, because nighttime HRV is the most reliable window for tracking long-term recovery and nervous system health. The ring also supports a live HRV reading on demand during the day, for users who want a spot check.
HRV is deeply personal. Numbers vary widely by age, fitness level, gender, and lifestyle. A reading that is normal for one person can be high or low for another. This is why Circular Ring 2 builds your own personal reference HRV instead of comparing you to a population average.
HRV is one of the most responsive signals your body produces. Sleep, stress, training intensity, alcohol, late meals, illness, travel, and emotional load all show up in your HRV. That sensitivity is exactly why HRV is useful as a readiness signal.
Yes. HRV is one of the signals behind your Energy Score, together with activity, sleep, resting heart rate, temperature, blood oxygen, and breathing rate.
Kira AI generates one personalized, actionable recommendation a day, on demand. Daily summaries appear automatically, and pattern detection runs continuously in the background.
No. Kira AI does not diagnose conditions, prescribe treatment, or replace medical professionals. It translates biometric signals into lifestyle and behavioral guidance you can act on. For anything clinical, the Circular app generates PDF reports and trend summaries designed to be shared with your doctor.
Yes. You can log notes about travel, caffeine, alcohol, illness, workouts, late meals, and stress events. Kira folds these into her interpretation, which sharpens the accuracy and relevance of her recommendations.
Yes. We encrypt data between your ring, the app, and our cloud systems. We do not sell your health data or use it for advertising, though we process and share limited data when needed to run, protect, and improve the service.
Yes. Kira AI reads training loads against recovery and energy trends and generates actionable pacing recommendations. This is particularly useful for athletes managing cumulative fatigue across training blocks or peaking for competition.
Circular Ring 2 is not intended to diagnose, treat, cure or prevent any disease, and is not for use in an emergency.
Take a reading whenever you want one. No subscription, no limit.
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