Ugh, the Apple Watch Compare page still doesn't have a drop-down with old models.
SE vs. old SE:
- now starts at $249, down from $279. However, the $199 Series 3 is gone, so the minimum price is up.
- cardio fitness notifications (maybe this is a watchOS 9 feature, though)
- cycle tracking
- crash detection
- compass backtrack + waypoints
- international roaming on the cellular model
- new back case design
- sleep stages (maybe this is a watchOS 9 feature, though)
- S8 instead of S5
- high-g accelerometer
Some nice stuff, but not a big upgrade. For example, even the Series 4 had an always-on display and ECG; the new SE still does not.
Series 8 vs. Series 7:
- no more titanium option; that's Ultra-only (at least this time)
- sleep stages (maybe this is a watchOS 9 feature, though)
- Cycle tracking with retrospective ovulation estimates
- compass backtrack + waypoints
- international roaming on the cellular model
- temperature sensor (seems to be only for ovulation detection for now?)
- S7 instead of S7, but it's unclear what if anything this changes
- high-g accelerometer
Ultra vs. Series 8:
- stupid name
- ugly button island on the right
- left-side customizable button
- 2000 nits instead of 1000. That's cool.
- 49mm instead of 45 or 41
- 100m water resistance instead of 50m
- dive to 40m
- depth gauge with water temperature sensor
- 86-decibel siren
- dual-frequency GPS instead of single-frequency
- 36-hour battery life instead of 18
- titanium instead of aluminum or stainless steel
- three-mic array with beamforming; S8 is apparently single-mic
- always cellular
- dual speakers instead of single; 40% louder
- Bluetooth 5.3 instead of 5.0. That's… strange.*
*) either the Ultra has 5.3 because it needs something in it, or the S8 and SE only have 5.0 because lots of internals didn't receive an upgrade this year.