Support

Common questions

Which Apple Watch starts rounds automatically?

Any watch with a water temperature sensor: Apple Watch Ultra, any generation, and Series 10 and later. On those, getting into water starts a round and the measured temperature decides whether it is hot or cold. Every other Apple Watch model works fine — you pick each round by hand with the Switch button, and everything else is identical.

Why did my sauna round not start by itself?

A sauna never submerges your wrist, so there is nothing for the sensor to read. The same is true of a hot or cold shower. Those three are always picked by hand; only a bath and a plunge can be detected. Cold or hot is read from water temperature, which means water.

The watch said “reading” for the first few seconds. Is that a fault?

No. The watch case starts near body temperature and takes several seconds to equalise with the water, so the first readings are the case rather than the bath. Contrast ignores a reading until the uncertainty the sensor reports drops below 1.5 °C, then needs three consecutive agreeing samples before it commits to a phase. The round still counts from when you got in.

My bath registered as neither hot nor cold. Why?

Water at or below 20 °C classifies as cold and at or above 33 °C as heat. Between the two is a deliberate dead zone, because real contrast therapy leaves a wide gap between the two states and a fine-grained call there would be guessing. Both thresholds are yours to change in Settings if your bath genuinely sits in between.

I walked off without ending the session. What happens?

It ends itself after five minutes of rest by default, and the end is back-dated to when you actually stopped rather than to when the timer noticed. The rest timeout is adjustable from one minute to three hours, and a round that runs past 90 minutes also closes. Tapping “still going” when the watch asks buys another ten minutes.

What does Contrast write to Apple Health?

Each session is saved as a Cooldown workout with its heart rate and water temperature samples. Contrast also keeps its own copy of every session on your iPhone, so deleting the workout from Health does not lose it from your history, and you can write it back. Settings and edits sync between your phone and watch through your own iCloud.

Where is my data stored?

On your devices, in your own Apple Health, and in your own private iCloud. There is no account and no server of ours. Nothing is sent to Fluctus Limited, and we cannot read, recover or restore your data.

Do archived sessions still count?

No. An archived session is excluded from Analysis, from the weekly goal and from the coach. It stays in Apple Health, because Contrast does not delete anything from Health on your behalf.

No Apple Watch. Can I still use it?

Yes. Time a session on the iPhone as it happens, or log a past one afterwards: when it started, each round, and the temperatures if you know them. Manual logging is free and always will be.

What is free and what is Pro?

Free, permanently: tracking on your watch, saving to Apple Health, logging by hand, your last 7 days of sessions, your weekly sauna, cold and heat set against published research, and an explanation of every metric. Contrast Pro adds your full history, the heart rate and water temperature charts, time in each temperature band, heart rate zones, sauna temperature, combining and archiving sessions, and the Analysis tab beyond the weekly amounts.

How do I cancel a subscription?

In your Apple Account settings on your device: Settings → your name → Subscriptions. Cancelling stops the next renewal and leaves the period you have already paid for intact. The lifetime option is a one-time purchase and has nothing to cancel.

Why does the app not show calories for a sauna?

Because the number would be wrong. Heat raises your heart rate by moving blood to the skin rather than by working muscle, so the usual heart-rate-to-calories conversion does not hold in the heat — a point the research is explicit about. Contrast reports the minutes your heart spent at moderate and vigorous rates and stops there.

Is there an Android or web version?

No. Contrast is iPhone and Apple Watch only. The water temperature sensor, HealthKit and the sync between phone and watch are all Apple platform features.

Safety, and what this app is not

Contrast is not a medical device. These metrics describe your sessions and set them next to published research; they are not a diagnosis or medical advice. Some are Contrast’s own measures, and each page says how strong its evidence is. Check with a doctor before starting sauna or cold exposure, especially if you have a heart condition, high or low blood pressure, or are pregnant.

Two things worth repeating, both of which the app says on its own metric pages. Cold water is most dangerous in the first minute, when the gasp reflex peaks; very cold water can make it hard to move within about ten minutes, and your body temperature keeps falling for a while after you get out. Sauna is well tolerated by most healthy adults, and unstable angina, a recent heart attack and severe aortic stenosis are reasons to avoid it. Alcohol raises the risk of low blood pressure and arrhythmia in a sauna.

Nothing in Contrast is a target. The weekly goal presets are named after the studies they come from, and the app calls them starting points rather than prescriptions.Every metric states its own limits.

Still stuck?

Email support@fluctusltd.info with any question about the app. Include your watch model and, if it is about a specific session, roughly when it was.

Please do not send screenshots of your health data unless a question genuinely needs them. Your sessions live on your devices and in your own iCloud, and they are better off there — we cannot read them, and we would rather not have a copy sitting in an inbox.

Legal

Privacy policy and terms of use, both on the company site.