ContrastAn iPhone and Apple Watch app for sauna, hot bath and cold plunge. Getting into water starts a round on its own, with heart rate and water temperature, and every metric shows its method and its evidence.https://contrastapp.info/en-usWhen a session ends itself, and why the clock runs backwardshttps://contrastapp.info/blog/when-a-session-ends-itself/https://contrastapp.info/blog/when-a-session-ends-itself/Walk off without tapping End and Contrast closes the session after five minutes of rest — back-dated to when you actually stopped, not when the timer noticed.Sun, 20 Sep 2026 00:00:00 GMTgetting-startedauto-endsession-lengthwater-lockLogging a sauna session without an Apple Watchhttps://contrastapp.info/blog/logging-without-a-watch/https://contrastapp.info/blog/logging-without-a-watch/Time a session live on the iPhone, or log one after the fact with its rounds and temperatures. Manual logging is free and always will be.Fri, 18 Sep 2026 00:00:00 GMTgetting-startedmanual-loggingno-watchfree-tierWhat Contrast writes to Apple Health, and what it keepshttps://contrastapp.info/blog/what-contrast-writes-to-apple-health/https://contrastapp.info/blog/what-contrast-writes-to-apple-health/Every session is a Cooldown workout with heart rate and water temperature. A second copy stays on your iPhone, so deleting the workout loses nothing.Wed, 16 Sep 2026 00:00:00 GMTgetting-startedapple-healthhealthkitprivacydataSix water temperature bands, and the gap between themhttps://contrastapp.info/blog/six-water-temperature-bands/https://contrastapp.info/blog/six-water-temperature-bands/Icy, Cold, Cool, Warm, Hot, Very hot — and nothing at all between 20 and 33 °C, because nobody soaks at 26.Mon, 14 Sep 2026 00:00:00 GMTgetting-startedtemperature-bandswater-temperaturecold-plungeSauna, bath, plunge, shower: why only two can be detectedhttps://contrastapp.info/blog/sauna-bath-plunge-shower/https://contrastapp.info/blog/sauna-bath-plunge-shower/Contrast has four modalities and a water sensor that can only see two of them. A sauna is dry and a shower never submerges the wrist.Sat, 12 Sep 2026 00:00:00 GMTgetting-startedmodalitysaunacold-plungeshowerHow an Apple Watch knows you got into cold waterhttps://contrastapp.info/blog/how-the-watch-knows-youre-in-water/https://contrastapp.info/blog/how-the-watch-knows-youre-in-water/Three gates stand between a temperature reading and a round starting: the sensor settling, a threshold at 20 °C or 33 °C, and three samples agreeing.Thu, 10 Sep 2026 00:00:00 GMTgetting-startedwater-temperature-sensorapple-watch-ultraautomatic-rounds