Skin Temperature

Skin Temperature — cycle awareness, body clock & illness heads-up

Your WHOOP streams skin temperature every night, and NOOP already banks it. v5 reasons from that one signal three ways, entirely on your device, free and private: a coarse menstrual-cycle phase, a body-clock / jet-lag helper, and a smarter illness early-warning that doesn't cry wolf. These are features other apps sell as a cloud subscription — and the data that's most sensitive (cycle, illness) is exactly the data NOOP keeps physically on your device.

All three live in Health → Skin temperature.

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What you need

• A few nights of overnight wear so NOOP can learn your personal nightly baseline. Cycle awareness needs roughly one to two cycles before it reads confidently; the body clock needs about a week.
• Each feature shows an honest confidence chip (Solid / Building / Learning your pattern) and says "no clear pattern" rather than guessing.

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1. Cycle awareness (opt-in)

A coarse menstrual-cycle phase read from your nightly skin temperature, corroborated by your resting-HR and HRV pattern (temperature and resting HR run a touch higher, HRV a touch lower, in the luteal phase).

Turn it on:

1. Open Health → Skin temperature.
2. On the cycle card, tap "Turn on cycle awareness."
3. Wear your strap overnight. As NOOP learns, the card shows your phase — Follicular / Peri-ovulatory / Luteal — with a confidence chip and a small thermal sparkline.
4. (Optional) Tap "Log period start" to anchor it to your real cycle and sharpen the estimate. It's stored only on this device.

How to read it honestly: this is awareness only — not contraception, not a fertility predictor, not a medical service. It never gives "fertile" or "safe" days. A period estimate is always a window ("likely in the next few days"), never a hard date. If your pattern is flat or irregular, NOOP says "no clear pattern" rather than inventing a phase. Pregnancy, hormonal contraception, perimenopause, PCOS and shift work all flatten or distort the signal, and NOOP says so plainly.

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2. Body clock (jet-lag / shift helper)

NOOP estimates your body-clock phase from your nightly temperature low and your rest-activity rhythm, and shows how far it sits from your schedule — e.g. "About 25 min later than your schedule."

1. Open Health → Skin temperature and find the Body clock card.
2. Read the lean ("a night-owl lean") and the estimated body-clock low time.
3. Tap "Plan a trip or shift" to enter a destination time-zone offset or a new shift pattern. NOOP gives a day-by-day light + sleep-timing plan ("Day 1: morning light 07:00–08:00, lights-out 22:45") to close the gap a step at a time.

How to read it honestly: it's behavioural awareness — light and sleep timing only, never melatonin or any supplement. If your schedule is irregular, it says "hard to read right now" rather than forcing a number.

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3. Heads-up (illness early-warning)

The old illness banner could fire after a night out. The new one scores how far your resting HR, HRV, skin-temp and respiration have drifted in the illness direction — and cross-checks your journal to rule out the obvious confounders.

Turn it on: Settings → Automations → "Illness early-warning."

When it has something to say, it shows a calm banner with:

• The why: "RHR +6, HRV −22%, skin temp +0.7 °C."
• What it ruled out: "With no alcohol or travel logged…"
• A downgrade when a confounder explains it: if you logged alcohol, a sauna, stress or travel, it reads "Probably not illness — you logged a few drinks" instead of alarming you.
• If you already logged feeling unwell, it switches to "Rest up — your numbers agree."

How to read it honestly: it's "a heads-up to rest," never a diagnosis. It never names a condition and always carries "On-device estimate — not a diagnosis." It only speaks up once it has a trusted baseline; below that it stays quiet.

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Privacy

This is the headline, not the fine print. There is no cloud, no account, no telemetry — so your cycle, illness and temperature data is physically incapable of leaving your device. Cycle awareness can be turned off at any time, which deletes the period data you logged. For sensitive health data, "it never leaves your wrist" is a promise only a local-first app can make truthfully.