The thinnest health tracking ring you can wear 24/7 without noticing
Visit Circular →The Circular Ring Slim stands out in the crowded smart ring market as one of the thinnest options available, measuring just 2.2mm thick — roughly the thickness of two credit cards stacked together. French-based Circular has built its reputation on creating wearables that disappear on your finger, and the Slim model delivers on that promise with an aerospace-grade titanium shell that weighs as little as 2.5 grams depending on size. After wearing it continuously for three weeks, we barely noticed it was there, even during typing, weightlifting, and overnight sleep tracking. The ring packs an impressive array of sensors into its slender frame, including PPG optical heart rate monitoring, skin temperature tracking, and a 3-axis accelerometer. Battery life comes in at around 4 days per charge, which is shorter than competitors but understandable given the tiny form factor. The companion app offers sleep staging, daily readiness scores, activity tracking, and menstrual cycle predictions, all without requiring a subscription — a refreshing change in this category.
At just 2.2mm thick and weighing 2.5-3.5 grams, the Circular Ring Slim is one of the most discreet wearables on the market. The aerospace-grade titanium shell is both incredibly strong and surprisingly light, making it the most comfortable smart ring for all-day and overnight wear.
Tracks light, deep, and REM sleep stages along with sleep duration, efficiency, and interruptions. The ring uses heart rate variability and movement data to generate a daily sleep score, with insights on how to improve your rest quality over time.
Continuous skin temperature monitoring detects subtle changes that can indicate illness, stress, or menstrual cycle phases. The built-in cycle prediction feature is especially useful for anyone tracking fertility or managing reproductive health.
Unlike Oura and many competitors, Circular Ring Slim includes all core features — sleep tracking, readiness scores, activity tracking, and temperature monitoring — without any ongoing subscription. What you see is what you get, with no hidden costs.
| Material | Aerospace-grade titanium |
|---|---|
| Thickness | 2.2mm (ultra-slim profile) |
| Weight | 2.5-3.5g (size-dependent) |
| Width | 7.5mm |
| Sensors | PPG optical sensor, skin temperature sensor, 3-axis accelerometer |
| Tracked Metrics | Sleep stages, HR, HRV, body temperature, activity, steps, calories |
| Battery Life | Up to 4 days |
| Charging | Magnetic USB charger, ~60 min to full |
| Water Resistance | IP68 (swim-proof up to 50m) |
| Subscription | None required |
| Price | $279 |
| Feature | Circular Ring Slim | Oura Ring Gen 4 | RingConn Gen 2 |
|---|---|---|---|
| Starting Price | $279 | $349 | $299 |
| Subscription Required | No | Yes ($5.99/mo) | No |
| Thickness | 2.2mm | 2.55mm | 2.8mm |
| Battery Life | 4 days | 7 days | 10 days |
| Material | Titanium | Titanium | Stainless steel |
| Sleep Tracking | Good | Best-in-class | Excellent |
| Temperature Tracking | Yes | Yes | Yes |
| Best For | Comfort & thin profile | Sleep accuracy | Battery & value |
Absolutely. At just 2.2mm thick and weighing as little as 2.5 grams, this is the most comfortable smart ring we've ever tested. We wore it continuously for three weeks — typing, lifting weights, sleeping, showering — and barely noticed it was there. The rounded inner edge prevents any pinching or discomfort, even during long workdays at a keyboard.
It's shorter than competitors, but manageable. In our testing, we consistently got 3.5-4 days between charges, which means charging once or twice a week depending on usage. The magnetic charger tops it up in about an hour, so it's easy to charge while you're showering or getting ready in the morning.
Yes, the Circular Ring Slim works with both iOS 13+ and Android 8.0+. The companion app is available on both the Apple App Store and Google Play Store, with feature parity across both platforms. You'll need Bluetooth 5.0 or later on your phone for the best connection experience.
Yes, the ring carries an IP68 water resistance rating, meaning it's fully dust-proof and can be submerged in water up to 50 meters deep. We tested it during swimming, showering, and even a hot tub session without any issues. Just be aware that the optical heart rate sensor won't work accurately underwater.
The Circular Ring Slim earns our recommendation for buyers who prioritize comfort and discreet design above all else. At just 2.2mm thick, it genuinely disappears on your finger in a way no other smart ring can match. The no-subscription pricing model is also a major plus, saving you roughly $72 per year compared to Oura. The tradeoffs are real — shorter battery life and sleep tracking that's good but not best-in-class — but if you want a ring you'll forget you're wearing, this is the best option on the market in 2026.
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