FurologWhich Apple Watch models have a water temperature sensor?
Not every Apple Watch can measure the water it is in. Here is which models have the sensor, how it works, and why it matters for logging onsen and sauna sessions.
Updated September 4, 2026
If you want your Apple Watch to record the temperature of the bath you are sitting in, you need one of the models that ship with a water temperature sensor. It is not a software feature. Older watches cannot be updated into having it.
Apple Watch Ultra (every generation), Series 10, and Series 11 have a water temperature sensor. Series 9 and earlier and every Apple Watch SE do not, and no update adds it. The sensor only reads while the watch is submerged, and Apple publishes a water temperature range for it only on Ultra: 0 to 40°C.
Which Apple Watch models have a water temperature sensor?
Apple introduced the sensor with the first Apple Watch Ultra in 2022 and brought it to the regular line with Series 10 in 2024. Every model since has kept it, and Apple's Depth app guide lists the supported models as Series 10, Series 11, and the Ultra models.
| Model | Water temperature sensor |
|---|---|
| Apple Watch Ultra, Ultra 2, Ultra 3 | Yes |
| Apple Watch Series 10, Series 11 | Yes |
| Apple Watch Series 9 and earlier | No |
| Apple Watch SE (all generations) | No |
The sensor sits alongside the depth gauge and was introduced for water activities. Apple publishes a water temperature range for it only on Ultra: 0 to 40°C for underwater activities, repeated as the "dive operating temperature" in the Ultra 3 specifications. The Series 11 specifications list the sensor but give no water temperature range. Furolog uses the sensor to record bathing water on supported models, and readings above that range, which is where most onsen sit, are not guaranteed by Apple.
How the sensor works
The watch has a small temperature sensor exposed to the water on the underside of the case. When the watch detects that it is submerged, the sensor starts reporting readings; Apple's own description is that it "measures the temperature of the water once Apple Watch has been submerged". Out of the water it does not measure anything, so you will not get air or sauna temperatures from it.
Two practical details:
- It needs a moment to settle. The first few readings after you step in lag behind the real water temperature as the sensor warms up. In our sessions it takes about half a minute to reach a stable number.
- It measures where your wrist is. In a large bath with a hot inlet on one side, moving your arm changes the reading. That is the water, not a bug.
What this means for Furolog
Furolog uses this sensor to log the bath temperature every five seconds for the entire session. That is where the temperature charts, the thermal contrast between hot soak and cold plunge, and the season by season trends come from.
Automatic water detection relies on the same underwater hardware. So for the full hands-free experience, where recording starts the moment you step in, you want one of the models in the table above.
Which one should you buy for bathing?
If temperature logging is the reason you are upgrading, any of the models in the "Yes" row above will do the job equally well. The sensor is the same across them.
The Ultra models are rated to 100 m and have the larger, brighter display, which is nice for reading heart rate in a dim sauna. Series 10 and 11 are thinner and lighter, which matters if you want to forget the watch is there during a long soak. Both are fine choices for onsen. Just remember that hot springs and heat are hard on any watch, so rinse it in fresh water afterwards.
Read next: Can you wear an Apple Watch in an onsen? · Apple Watch in the bath and sento: what's safe
Sources
- Apple Newsroom. "Introducing Apple Watch Ultra." 7 Sep 2022.
- Apple Newsroom. "Introducing Apple Watch Series 10." 9 Sep 2024.
- Apple Support. "Measure underwater temperature, duration, and depth on Apple Watch." Apple Watch User Guide.
- Apple Support. "Keep Apple Watch within acceptable operating temperatures."
- Apple. "Apple Watch Ultra 3, Technical Specifications."
- Apple. "Apple Watch Series 11, Technical Specifications."
- Apple Support. "About Apple Watch water resistance."
Quick answer
- Has the sensor: Ultra, Ultra 2, Ultra 3, Series 10, Series 11.
- Does not: Series 9 and older, all SE models.
- Published range: 0 to 40°C, for Ultra only. Series 10 and 11 have no published water temperature range.
- Furolog: records temperature every five seconds and starts automatically when you step into the water on the supported models.
