They explicitly only mentioned accelerometer. If they used more sensors, in particular temperature sensor, it's hard to imagine they wouldn't mention in, especi

They explicitly only mentioned accelerometer. If they used more sensors, in particular temperature sensor, it's hard to imagine they wouldn't mention in, especially that it would justify them limiting the feature to Series 9 and 10. However, reading on PAT (Peripheral arterial tone) and existing FDA-approved devices using that, they indeed use oxygen but not temperature. See for example "WatchPAT ONE" device.