Three zones set from your own alert threshold, and a tap on the wrist when it is time to step out.
Z3 · High
Z2 · Heat Stress
Z1 · Warm Up
History and consistency
Compare sessions, see your weeks as a heatmap and watch your total time in the heat add up.
Time in the heat42 h 15
Prepare and rehydrate
How much sweat a session costs you, what to drink back and the sodium, potassium and magnesium you lost.
To drink0.8 L
Na⁺690 mg
K⁺160 mg
Mg²⁺12 mg
iOS 26
Your heat, on the Lock Screen
Widgets for the Home and Lock Screen, a Live Activity while you are in the heat, and a control to start a session from Control Center.
Activity
Last session
Weekly benefit
Live Activity
Control Center
0 – 100
Every session, scored
A score out of 100 for heat, rounds, cooling and hydration, with your personal bests and your heat age right after you log it.
Badges
Badges that mean something
Volume, time in the heat, streaks: 29 medals earned session after session, without a single notification to beg you back.
Coming in 1.8.2
Your heat age, and what a year of sessions says.
One number for how your body handles heat, a training log that compares months, and your month told as stories, with the photos of your sessions.
Free
Your heat age
From your sessions, resting heart rate, VO2max and sleep: the age your body handles heat like, its pace over the months and what moves it.
Pro
Training log, month against month
Time in the heat, rounds, hottest session and recovery, this month against the last. See where the habit holds and where it slips.
5 h 15Last month
6 h 40This month
Pro
Your month, told as stories
Thirteen cards for the month: hottest session, best sleep after a sauna, your heat age, with the photos you took in the sauna.
Hottest session: 96°
The best sleep came after Thursday's sauna
18 h in the heat this month
Sauna Metrics Pro
Sauna Metrics Pro, a week free
The timer, the journal, the score, your heat age, widgets and badges stay free. Pro adds what needs Apple Health and the watch. Then a monthly or yearly subscription, or a one-time purchase.
Reviews copied word for word from the App Store, in the language they were written in: the most recent ones, whatever their rating. We don’t check them beyond what Apple does.
Free to download. Sauna Metrics Pro adds the Apple Watch app, the Health analyses, the training log and the recaps, with a free week to try. No account and no ads.
Sauna timer and log app for iPhone 
