4 and above, including the newer SE have fall detection, heartrate monitor, and ECG. Will also keep track of their daily activities standing, walking, exercise.

I think 8 has temp detection.

No need to pay for the 8 ultra unless you are climbing Everest IMO. Not worth the price just for Health monitoring.

Edit to add: I find the walking and standing reminders are great for avoiding clots that can lead to strokes if they sit or lay down too much.