The in-session telemetry app
Built around wearing an Apple Watch during the session: live heart rate, calorie tracking, and time-based “Benefit Zones” that segment a sit into warm-up, core heat, and later phases. Covers traditional, infrared, and steam saunas plus cold plunge, cold shower, and hot tub logging, and syncs to Apple Health. By its own listing it has logged over 100,000 sessions — the most visible pure sauna tracker on the App Store going into 2026.
The trade-off is the premise itself. Apple rates the Watch to 35°C ambient and a sauna runs at 80–95°C, and elevated heart rate under heat stress is a physiological constant rather than a personal insight. If what you want is in-session numbers, this app is the most complete way to get them — but it tells you what happened during the heat, not what the heat did to you afterward.
Best for: live in-session stats on an Apple Watch you're willing to wear in the heat.
The session diary
A deliberately simple digital sauna diary, and a long-running favorite in the traditional sauna community. You enter each session by hand — sauna type, temperature, humidity, duration, Aufguss, cold shower or plunge, heart rate — and HotLog turns the history into habit statistics and writes sessions to Apple Health as workouts. iCloud sync and CSV export are included.
What it doesn't attempt is any read on your physiology. There's no HRV, no sleep, no recovery signal — by design. It answers “how consistent is my practice?” and stops there.
Best for: a clean manual log of a traditional sauna habit, no wearable involved.
The community habit app
The social one. GoPolar logs cold plunges, cold showers, sauna, red light, and hyperbaric sessions with duration, temperature, heart rate, and reflections, works with Apple and Garmin watches, and wraps it in a community layer — location discovery with check-ins, challenges, badges, and a feed of other people's sessions.
It leans cold-first: user reviews note that the sauna side is largely manual entry. If accountability and community keep your practice alive, it's the strongest pick here. It doesn't attempt outcome attribution — the question of whether the practice is moving your HRV, resting heart rate, or sleep is out of scope.
Best for: streaks, challenges, and finding plunge and sauna spots near you.
Ours, for the record
Sauna Score
The other three help you answer “what did I do?” Sauna Score is for the next question, “is it working?” It reads the HRV, resting heart rate, and sleep your wearable already writes to Apple Health, then compares the weeks you kept your protocol against the weeks you didn't, the same comparison the Laukkanen cohort study used. The protocols are named and cited (Laukkanen 2015 in JAMA Internal Medicine, Søberg 2021 in Cell Reports Medicine, the Japanese tōtōnoū ritual), every number comes with a confidence band, and the daily readiness reading (go hot, go gentle, or skip) is built from your own baseline.
There's one thing it deliberately leaves out: in-session tracking. No wearable really survives 80–95°C, so Sauna Score reads your morning baseline before the session and your overnight recovery after instead. The end-of-session alarm is a Time-Sensitive iOS notification that reaches you through a locked phone and Focus modes.
Best for: wearable owners who want to know whether the practice is actually moving their numbers.
Download for iOS / Android
