Your chest strap already knows how you slept. NoctaliX records your heart overnight with the Bluetooth chest strap you train with and turns it into HRV, sleep stages and a morning readiness score, written straight into your Intervals.icu wellness data.

No new ring or band to buy. No ads. Free, coach included.

WHY A CHEST STRAP
Rings and watches estimate each heartbeat by shining light through the skin. A chest strap reads the heart's electrical signal, so beat-to-beat (RR) intervals, the raw material of heart rate variability, come out far cleaner. NoctaliX puts the strap you already trust for your workouts to work for the other eight hours.

WHAT YOU WAKE UP TO
- Readiness score: last night compared with your own baseline, so you know whether today is for intervals or an easy session
- HRV: rMSSD, SDNN and pNN50, with artifacts and ectopic beats filtered out before any calculation
- Resting heart rate: lowest and average heart rate across the night
- Sleep stages: deep, light, REM and time awake, estimated from your heart rate dynamics, plus the accelerometer if you use a Polar H10
- A data quality rating for every night, so you know how far to trust the numbers

TRAINING COACH
The coach reads your night and your training load and plans your swim, bike and run sessions in your Intervals.icu calendar, adjusting them when your body says you're not recovered. Intervals.icu can then send the sessions to your watch.

NOCTALIX AGE
An estimate of how old your heart behaves, based on your overnight data and fitness, and how it moves as your training does.

WORKS WITH INTERVALS.ICU
NoctaliX writes each night to its own wellness fields, so it won't overwrite data you already sync from other devices or apps.

BUILT FOR AN 8-HOUR RECORDING
Recording runs in the background all night with a visible notification, reconnects on its own if the signal drops, and can start automatically when you put on your paired strap.

YOUR DATA STAYS ON YOUR PHONE
Recordings are processed on the phone. Your nightly summary goes only to your own Intervals.icu account. No analytics, no crash tracking, no ads, and nothing the developer can read.

WHAT YOU NEED
- An Android phone with Bluetooth
- A Bluetooth chest strap that sends RR intervals, such as Polar H10 or H9, Wahoo TICKR, CooSpo and many others
- An Intervals.icu account (a free account works)
- Your phone on charge by the bed

Sleeping with a strap takes two or three nights to get used to. Wear it a notch looser than when you train.

NoctaliX is designed for training and wellness. It is not a medical device and doesn't diagnose or treat any condition.

Questions or feedback: hello@noctalix.com