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Try the prototype for 10 to 15 minutes. It's best on a laptop or desktop, where the iPhone and Watch sit side by side.
Tap how each screen feels as you go, then answer a few questions. Everything saves by itself, so there's nothing to send.
One quick step: open this page in Safari or Chrome. Google won't let you sign in inside this app's built‑in browser. Tap ••• or the share icon, then choose Open in browser.
On your phone? It works here too, but the prototype is much easier on a bigger screen. Send yourself the link and open it on your laptop.
Signing in shares only your name and email address with me, nothing else from your Google account. Your answers go into a private database that only I can read. I use them only for this research, and I'll delete them whenever you ask.
Before you start · 1 minute
A bit of context first
Heat, cold, or both
Heat is a sauna, a steam room or a hot shower. Cold is an ice bath, a cold shower or a swim in the sea. Some people do just one. Others switch between them for a few rounds, with a rest in between. That's contrast therapy.
People do it at a studio, at the gym or at home. They do it for how it feels, to switch off, after training, or for their health in the long run.
Most people do it on instinct. There's no plan, no record, and by the next day the details are gone. Leuto is for all of it. It records what you did and shows how your body responded, compared only with your own earlier sessions.
Your role
If you already do heat or cold, just be yourself. When the app asks what you have, pick what's true, even if it's only a hot shower.
Never tried any of it? Then picture this.
You work out a few times a week, and a friend got you into a studio with a sauna and an ice bath. Your first session is on Saturday. You've just downloaded Leuto to guide you, and you're curious how your body will handle it.
How the test works
Explore. Leuto is right there on screen, clickable, with made-up data. Tap around like you would with an app you just downloaded. Not everything works yet, and that's fine.
React. Under the phone, a small label says which screen you're on. The panel next to the appThe bar at the bottom of your screen shows the same screen. Tap how it felt, and add a few words.
Tell me. A few quick questions at the end. Your answers save as you go, so you can stop anytime and come back later.
About 15 minutes
SCREENSession complete
After a session
Loved itFineConfusingBroken
The panel always matches the label under the phone.
··
Hi, thanks for doing this
Tear it apart. That's what this test is for.
Your answers are all still here. One thing is new. The panel now follows the screen you're on, so you can rate each one as you go.
The controls above the phone
Everything in the prototype is made-up demo data, so click anything. Nothing you do there is saved.
Leuto is the app's working name.
The Watch is pretend too. The buttons under it turn the Crown and take it off or put it back on.
Subscribing is pretend. Nothing is ever charged.
Tap a selected answer again to clear it.
Device
Leave it on iPhone. The other devices are design explorations.
Look
Light or dark.
Plan
Free or Premium. Guided sessions need Premium.
Simulate
Pretend you have no Watch, didn't share Apple Health, or the Watch lost your heart rate.
User
First time, or Returning with a few weeks of sessions behind you.
Time
Morning or evening. Today's suggestion changes with it.
Speed
×20 fast-forwards a running session so you don't wait 15 minutes.
Interrupt
Pretend the app closed in the middle of a session.
Onboarding
Replays the first-run intro.
Reset app
Starts over from scratch.
Why I'm building this
Prototype · demo data
On your phone? It's roomier on a laptop. Sign in there with the same Google account and your answers come with you.
Hi 👋, my name is Thanh, and I do heat and cold, often back to back. And I keep wondering what it's doing to my health in the long run. How does my body actually react? Is it doing me any good?
A feeling can't tell you that, and the long-term research is thinner than the hype.
So I'm building the app I wanted, for heat, cold or both. It times every phase, even while your Watch is off in the sauna. It captures how your body reacts in the cold and how long your heart rate takes to settle. And session after session, it shows how that changes, against your own history and nobody else's.
There's a Learn section too, built on the research. Every card says how strong the evidence is, and the finished app will link the studies so you can go deeper.
Before I build the real thing, I want to know if you'd use it. Be blunt.