How a ring reads what a watch guesses.
Every number HSRing shows you comes from three sensors, one algorithm we can explain, and a fourteen-day baseline that belongs to you alone. This page walks through all of it.
The palm side of the finger is thin, warm and full of arteries.
Optical heart-rate sensing works by shining light into skin and measuring how much comes back with each pulse. On the wrist the light has to pass through tendon, fat and a wandering radial artery. On the finger it meets the digital arteries a few millimetres under the surface, with almost nothing in the way.
The result is a pulse waveform with roughly ten times the amplitude of a wrist reading at the same LED power. We spend that advantage on battery life and on resolving beat-to-beat intervals, which is what makes heart rate variability trustworthy.
Three sensors. Nothing you have to charge twice a day.
Green + red + infrared PPG
Three wavelengths at two depths. Green for heart rate and HRV, red and infrared for blood oxygen. Sampled at 250 Hz overnight, duty-cycled in the day.
Skin temperature, NTC pair
Two thermistors on the palm side, resolving 0.01 °C. We report deviation from your rolling baseline, not absolute temperature, because absolute skin temperature says more about your bedroom than about you.
3-axis accelerometer
Detects steps, workout onset, sleep onset and the micro-movements that separate light sleep from wake. Also the tie-breaker when the optical channel is noisy.
Every score has a recipe you can read.
We do not publish a black box. Each morning number is built from named inputs with stated weights, and the app shows the breakdown on tap.
Sleep staging
A gradient-boosted model over 30-second epochs. Inputs are HRV, respiratory rate derived from the PPG envelope, temperature slope and movement. Trained against polysomnography, tuned per user after seven nights.
Resting heart rate
The 5th percentile of overnight heart rate between 02:00 and 06:00, not the lowest single reading, so one artefact cannot move it.
Recovery score
Four normalised z-scores against your fourteen-day baseline: resting HR (35%), HRV (35%), temperature deviation (15%), sleep duration and efficiency (15%). The weights are fixed and shown in the app.
Sleep apnea risk
Counts overnight events where SpO₂ drops 3% or more for at least 10 seconds together with a heart-rate surge. Reported as events per hour, averaged over fourteen nights.
Against the reference
Internal study, 42 adults, 3 nights each, wearing HSRing alongside polysomnography and a chest-strap ECG. Figures below are agreement with the reference device. Full method and data on request.
| Metric | Reference | Agreement | Note |
|---|---|---|---|
| Heart rate | Chest-strap ECG | MAE 1.2 bpm | Overnight, all participants |
| HRV (RMSSD) | Chest-strap ECG | r = 0.96 | Five-minute windows, sleep only |
| Sleep vs wake | Polysomnography | 94% agreement | 30-second epochs |
| Four-stage sleep | Polysomnography | 78% agreement | Deep / REM / light / wake |
| SpO₂ | Clinical pulse oximeter | MAE 1.8% | Range 85–100% |
A nightly screen for something most people never get tested for.
Obstructive sleep apnea affects roughly one adult in seven and about 80% of cases are undiagnosed. HSRing looks for its fingerprint every night: repeated dips in blood oxygen paired with a brief heart-rate surge and a movement spike.
After fourteen nights the app shows a risk band (low, moderate, elevated) with the underlying event count per hour, and a one-page summary you can hand to a physician.
HSRing is a wellness device, not a medical device. The risk band is a screening aid and does not diagnose sleep apnea or any other condition. Talk to a clinician about any result that concerns you.
- LOW
- < 5
- events / hour
- MODERATE
- 5 – 15
- events / hour
- ELEVATED
- > 15
- events / hour
Measured on your finger. Kept on your terms.
Stored on the ring first
Seven days of raw samples live on the ring. Nothing depends on a live connection.
Encrypted in transit and at rest
End-to-end from ring to phone to our servers. Support staff cannot read your health data.
Never sold, never shared
No advertising partners, no data brokers, no insurers. Aggregate research use is opt-in and anonymised.
Export or delete any time
JSON or CSV export on request, and one-tap account deletion in the app. Deletion is permanent after a 30-day window in which you can change your mind.