Questions and Answers

Any Apple Watch can run sauna rounds and cold sessions with heart rate. Live water temperature, and starting a cold session automatically when you go in, need a Watch with a water temperature sensor: Apple Watch Ultra, Series 10 or Series 11.

No. The Watch runs the whole session and gives the warnings on your wrist, so your phone can stay in the locker. You set up the app, and look back at sessions, on your iPhone.

Heat and cold are risky for some people, for example with a heart condition or high blood pressure, or in pregnancy. The first launch asks a few questions, and any yes shows "talk to your doctor first" before you continue.

Three taps before each session: have you been drinking alcohol, do you feel unwell or feverish, and do you feel dizzy. Any yes makes today a skip day.

Choose how many rounds and when to step out. The Watch shows the round time and your heart rate, buzzes at your step-out time, then counts a rest while you sit down and sip water.

Start short and build up slowly. The app suggests a step-out time and you can set your own, but step out at once if you feel dizzy, faint, sick or have chest pain.

Only if you choose to. It is an opt-in, off by default, with plain warnings. High sauna temperatures can go beyond the operating limits Apple publishes for its Watches, so check Apple's guidance for your model.

No. The Watch cannot measure air temperature in a sauna, so the app never shows one. It shows your time in the heat and your heart rate.

Two minutes for your first five sessions, then three. You can raise your limit in steps up to five minutes. Ten minutes is a ceiling that cannot be changed. You feel a haptic warning at 80% of your limit and a repeating alarm at the limit until you tap Out.

No. The in-water screen is glanceable and uses haptics only, so Water Lock can stay on. On Watches with a water sensor the session notices when you get in and out.

The first 90 seconds after you get in. Stay still and let your breathing calm. The timer for your limit starts after it.

Breath holds and fast breathing near cold water are a drowning risk, so the app never prompts them. It only asks you to stay still and breathe slowly while you settle.

Cold water and movement can stop the Watch getting a reading. When that happens the app shows dashes rather than guessing, and never saves a zero.

A gentle look at your minutes in the heat and the cold this week, against a reference of about 57 and 11 minutes from published research. There are no streaks, and it never asks you to do more than is safe today.

Your body can keep cooling after you get out. The 45 minute rewarm walks you through drying off, dressing warm, a warm drink and waiting before a hot shower, and asks how you feel.

Choose a contact before a sauna or cold session. They get a short message when you start, and are told if you have not finished by your limit plus a margin. Only the session status is shared.

Yes. Export a CSV from the iPhone app, and delete any session, or everything, from the app and from Apple Health where the app wrote it.

Tidal Contrast is in development. The App Store link will be on this site when it is ready.

Only if a doctor has said that is right for you. The app treats heat and cold as separate sessions, with a rest or a rewarm after each.

No. It is a wellness tool. It does not diagnose, treat or prevent any condition, and it cannot keep you safe on its own.