Compare
Four ways to record a session
Most people already track this somehow. Each approach works, and each throws away one specific thing — usually the thing you wanted six months later.
| Stopwatch | Habit app | Apple Fitness | Contrast | |
|---|---|---|---|---|
| Times a round | Yes | Yes | Yes | Yes |
| Keeps a history | No | Yes | Yes | Yes |
| Separates rounds from rest | No | No | No | Yes |
| Knows hot from cold | No | Sometimes | No | Yes |
| Water temperature | No | Typed in | No | Measured |
| Starts without a tap | No | No | No | On Ultra / Series 10+ |
| Heart rate per round | No | Sometimes | Whole workout | Yes |
| Writes to Apple Health | No | Usually | Yes | Yes, as Cooldown |
| Method shown for each number | — | Rarely | — | Yes, with sources |
"Habit app" covers the general category of session loggers with a temperature field you fill in yourself; individual apps vary and several do more than this. Checked against App Store listings in September 2026.
The difference that is hard to copy
Apple Watch Ultra and Series 10 and later carry a water temperature sensor, and Core Motion exposes both a temperature and a submersion state to apps. As of September 2026 no App Store listing in this category mentions reading it.
Contrast does. Submersion starts a round; the measured temperature classifies it as hot at or above 33 °C, cold at or below 20 °C, with a deliberate dead zone between and three agreeing samples required before anything commits. The consequence is not precision for its own sake — the round starts when you get in, rather than when you remember to press something with wet hands.
What Contrast does not do
- No guided protocol. Several apps ship preset multi-phase plans that auto-advance with audio and haptics. Contrast records what you did rather than telling you what to do next.
- No community, challenges or badges. No feed, no sharing, no leaderboard.
- No streak counter. Cold water is a poor thing to manufacture urgency about.
- No calorie estimate for the heat. Heat raises heart rate by moving blood to the skin rather than by working muscle, so the usual conversion does not hold.
- No readiness or recovery score. A composite hides which input moved it, so you cannot check it. The longer reasoning is on the blog.
- No breathwork, no hardware control, no Android.
Which to choose
If you want a voice telling you when to switch, pick an app with a guided protocol. If you want a community, pick one with a community. If you do the same thing every week and never intend to ask a question about it, a habit tile is genuinely enough.
Contrast is for wanting to know, at the end of a month, exactly how many minutes you spent above 38 °C and whether your heart settles faster in cold water than it did in February — with every one of those numbers showing its working.
A longer comparison of the field is on the blog.