Made for the Action button
One press moves you to the next phase, even under Water Lock. Apple Watch Ultra is highly recommended.
App
Apple Watch & iPhone · By Dave Ellis
Sauna + Plunge Contrast therapy timer for Apple Watch
Sauna, cold plunge and the walk between, timed round by round on your wrist. On Apple Watch Ultra, one press of the Action button moves you on, even with wet hands and Water Lock on.
- 0 Press to the next phase
- 0 Phases, each in its own colour
- 0 Days of history, free
- 0 Accounts or trackers
Know where you are
Each phase has its own colour and each switch its own haptic, so you can tell without looking.
Heart rate, live
Your heart rate on your wrist as you go, beside the phase timer and the session total.
Saved to Health
Every session saves to the Health app as a workout, and your iPhone keeps the history.
Apple Watch · iPhone · watchOS 11 and iOS 18 or later · Made for Apple Watch Ultra
In short
What is Sauna + Plunge?
What is Sauna + Plunge?
Sauna + Plunge is a contrast therapy timer for Apple Watch. It times the sauna, the cold plunge and the walk between them, round by round, with your heart rate live on your wrist and a colour and a haptic for every phase.
It's made for the Action button on Apple Watch Ultra: one press moves you to the next phase, even with wet hands and Water Lock on, so you never need to touch the screen. On other Apple Watch models you tap Next instead. Every session saves to the Health app as a workout, and the iPhone app turns them into your history, a heart rate graph for each session, your all-time bests and your trends.
Sauna + Plunge is made by Dave Ellis, an award-winning web and mobile developer in Edinburgh, Scotland, and published on the App Store by The Racing Line Software Limited.
| What it is | A contrast therapy timer for Apple Watch, with an iPhone app for history and stats |
|---|---|
| Works on | Apple Watch with watchOS 11 or later, and iPhone with iOS 18 or later |
| Best on | Apple Watch Ultra, for its Action button (highly recommended) |
| Other Apple Watch models | Tap Next on the screen to switch phase; Water Lock stays off |
| Phases | Sauna, transition, cold plunge, transition, and back to sauna |
| On your wrist | The phase timer, the session total and your heart rate, live, with a colour and a haptic for each phase |
| Where sessions go | The Health app, as workouts |
| Price | Free to download. Sauna Unlimited is £2.99, once, with no subscription |
| Free version | The whole watch app; the last 30 days of history on iPhone |
| Sauna Unlimited | Your whole history, all-time bests, trends over months and years, and no banner |
| Account needed | No |
| Ads, analytics, tracking | No analytics or tracking. Free shows one small banner on iPhone for my other apps, like The Racing Line |
| Made by | Dave Ellis, Edinburgh, Scotland |
| Published by | The Racing Line Software Limited |
| App Store category | Health & Fitness |
| Help | Support · Privacy policy |
01
On your wrist
One press, and you're in the next phase.
Sauna + Plunge does the timing on your wrist, round after round, from the first press to the summary.
The Action button
On Apple Watch Ultra, each press moves you on: sauna, transition, cold plunge, transition, and back to sauna.
Under Water Lock
Presses still work with Water Lock on and wet hands, so you never touch the screen. Press and hold the Crown to clear it.
A colour for each phase
Ember for the sauna, ice for the plunge and dusk for the walk between, readable at a glance in the heat or the cold.
A haptic for each switch
A light tap into the transition, and a different one as you reach the sauna or the plunge, so you know where you are without looking.
Your heart rate, live
Your heart rate on the phase screen through every round, with the timer for the phase and the total for the session.
Pause, end, save
Pause or end from the Options page, then save the session to the Health app as a workout from its summary.
Set up the Action button
Five steps in your watch's Settings, and they're in the app too. On other Apple Watch models, you tap Next on the screen instead.
How to set it up
02
Screenshots
Sauna + Plunge, screen by screen.
The session happens on your watch. Your iPhone keeps it.
On Apple Watch Ultra
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Start
Press Start, or the Action button, and the first round begins.
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Sauna
The phase you're in and its timer, your heart rate, and the round and total underneath.
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Transition
The walk between, in dusk, showing where it leads: here, down to the plunge.
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Plunge
Ice blue for the cold, so you can tell where you are at a glance.
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Options
Swipe across to pause or end. On Ultra, the Action and side buttons together pause too.
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Summary
Your total, your rounds and the time on each side, ready to save to the Health app.
On iPhone
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Every session, painted
Each session in the colours of its own rounds, with its time in the sauna, the plunge and between.
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Heart rate, round by round
Your heart rate through each round, in each phase's colour, with the average, the peak and the low marked.
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All-time bests
Most rounds, longest round and longest combined time, for the sauna and the plunge. With Sauna Unlimited.
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Trends
Time, rounds or heart rate over four weeks, or over months and years with Sauna Unlimited.
03
On your iPhone
Every session kept. Your bests, counted.
The iPhone app is the watch's companion. It reads your sessions from the Health app and shows you what they add up to.
Painted history
Every session in the colours of its own rounds, so you can tell them apart at a glance.
Heart rate, round by round
A graph of each session in each phase's colour, with the average, the peak and the low marked. Drag across it to read any moment.
Zoom to a round
Tap a round to zoom the graph to it, or a row in the session's timeline to zoom to that stretch.
All-time bests Unlimited
Most rounds, longest round and longest combined time for each side, and your longest session. Each best opens the session it came from.
Trends
Time, rounds or heart rate over four weeks, and over three months, a year or everything with Sauna Unlimited.
Delete a session
Delete a session on your iPhone and it leaves the Health app too, then your watch after the next sync.
The watch is never limited, and every session stays in the Health app either way. Free shows your last 30 days on iPhone; Sauna Unlimited shows all of them, straight away.
04
How it works
How to time sauna and cold plunge rounds on Apple Watch.
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Set up the Action button
On your watch, open Settings, tap Action Button, and set Action to Workout, App to Sauna and First Press to Sauna + Plunge.
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Press to start
Press Start, or the Action button, and the timer starts. Your heart rate shows as you go.
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Press for each phase
Each press moves you on: sauna, transition, cold plunge, transition, and back to sauna, with a haptic for each switch. Without an Ultra, tap Next.
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Save it and look back
Swipe to Options and tap End, then save the session to the Health app. Your iPhone shows its heart rate, your history and your bests.
05
Private by design
Your sessions stay in Health, not on a server.
Heart rate and the time you spend in the heat and the cold are personal. Sauna + Plunge saves your sessions to the Health app on your watch, and the iPhone app reads them from Health on your phone. There's no account, and no Sauna + Plunge server holding your sessions.
Free users see one small banner on iPhone for my other apps. It downloads from my own website without any identifier, and buying Sauna Unlimited removes it.
- No account: there's nothing to sign up for.
- Nothing collected: I never receive your sessions, your heart rate or anything else about you.
- Health, on your devices: read and written through Apple Health, and never used for advertising.
- No tracking: no analytics, no crash-reporting SDKs and no tracking.
- Deletes only what you delete: the iPhone app only changes Health to remove a session you delete.
- Bought through Apple: Sauna Unlimited is an App Store purchase, so I never see your payment details.
06
Free & Unlimited
Free on your wrist. Unlimited to keep all of it.
Free
The whole watch app. Your last 30 days on iPhone.
- Every phase, the Action button and live heart rate on Apple Watch
- Every session saved to the Health app as a workout
- Your last 30 days on iPhone, each with its heart rate graph
- Trends over the last four weeks
- Delete a session from your iPhone
Free shows one small banner on iPhone for my other apps, like The Racing Line.
Sauna Unlimited
Your whole history, and your bests.
- Every session you've saved, as far back as it goes
- All-time bests for the sauna and the plunge
- Your longest session
- Trends over three months, a year or everything
- No banner
£2.99 once, through the App Store. No subscription.
UK price shown; other countries see local prices on the App Store. Older sessions stay in the Health app either way, so Sauna Unlimited brings every one of them back as soon as you buy it.
07
Questions
Sauna + Plunge questions, answered.
What is Sauna + Plunge?
Sauna + Plunge is a contrast therapy timer for Apple Watch. It times the sauna, the cold plunge and the transition between them, round by round, with your heart rate live and a colour and a haptic for each phase. Sessions save to the Health app as workouts, and the iPhone app shows your history, bests and trends. It's made by Dave Ellis in Edinburgh, Scotland.
Do I need an Apple Watch Ultra?
No, but it's highly recommended. Only Apple Watch Ultra has the Action button, which moves you to the next phase with one press, even with wet hands and Water Lock on. On other Apple Watch models you tap Next on the screen instead, and Water Lock stays off so that you can.
How do I set up the Action button?
On your watch, open Settings, tap Action Button and set Action to Workout. Then set App to Sauna and First Press to Sauna + Plunge. Choose Sauna + Plunge rather than Open App, so each press switches phase during a session. The same steps are in the app.
Does it work under Water Lock?
Yes, on Apple Watch Ultra. The Action button keeps working with Water Lock on, so wet hands don't matter, and the app can turn Water Lock on for you. To clear Water Lock, press and hold the Digital Crown. On other models Water Lock stays off, because it would block the Next button.
How do I pause or end a session?
Swipe to the Options page and tap Pause or End. On Apple Watch Ultra, pressing the Action and side buttons together pauses and resumes too. When you end a session, its summary lets you save it to the Health app.
Does it show my heart rate?
Yes. Your heart rate shows live on the watch through every phase. On iPhone, each session gets a heart rate graph in the colours of its phases, with the average, the peak and the low marked.
Where are my sessions saved?
In the Health app, as workouts, with the sauna, plunge and transition times marked. The iPhone app reads them from Health, so there's no account and nothing is kept on a server.
Does the watch need my iPhone nearby?
No. The watch app runs on its own, so it times a session and saves it to Health without your iPhone. The session reaches your iPhone's History when Health syncs.
How much does Sauna + Plunge cost?
It's free to download, and the watch app is never limited. On iPhone, the free version shows your last 30 days, with a small banner for my other apps. Sauna Unlimited is £2.99, once, with no subscription: it unlocks your whole history, all-time bests and trends over months and years, and removes the banner.
Which devices does Sauna + Plunge work on?
Apple Watch with watchOS 11 or later, and iPhone with iOS 18 or later. It's made for the Action button on Apple Watch Ultra; on other Apple Watch models you tap Next. There's no Android version.
Does Sauna + Plunge collect my data or show ads?
I don't collect anything: there's no account, and your sessions and heart rate stay in the Health app on your devices. Free users see one small banner on iPhone for my other apps, like The Racing Line. It comes from my own website, not an ad network: nothing tracks you, and the app doesn't record whether you see or tap it. Sauna Unlimited removes it.
Who makes Sauna + Plunge?
Dave Ellis, an award-winning web and mobile developer in Edinburgh, Scotland, who also makes the motorsport app The Racing Line, the private location history app Location Vault and the custom widget maker Widgeling. Sauna + Plunge is published on the App Store by The Racing Line Software Limited.
Made by Dave Ellis
Sauna + Plunge is designed and built by Dave Ellis, an award-winning web and mobile developer in Edinburgh, Scotland. His motorsport app, The Racing Line, won Brand of the Year at the 2026 Race Media Awards and is used by more than 100,000 fans, and he also makes the private location history app Location Vault and the custom widget maker Widgeling. Sauna + Plunge is published on the App Store by The Racing Line Software Limited.
Questions or ideas? dave@daveellis.dev · More about Dave
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