I don't have a natural sleep schedule so it makes no sense for me to set one, it changes day by day and sometimes I don't even sleep.
Does the Apple Watch Series 8 track sleep without setting a schedule?
Yes - the watch generates all the data you need to track multiple naps or sleep intervals without setting a schedule or manually marking the start of sleep.
The app I use to track sleep automatically is AutoSleep and it will work for your needs.
I have used AutoSleep since before Apple included sleep focus and sleep schedules and it does everything you ask without needing to remember to set a focus, or change alarms or do anything except wear the watch and occasionally use the app on the watch / phone to validate and correct the algorithm. For me, the calibration works for 18+ months and it just manages to capture multiple sleep sessions a day when I nap or work well when I'm following a regular schedule. If I forget to open the app, I have complications on the Home Screen to remind me and it works even if I don't check in on the app but weekly at most (you can use it more often of course - just it doesn't need use to track the sleep once you set it up).
It integrates Apple's sleep analysis if you want but you don't need to do anything.
Here is a very good review of the "top three" third party sleep apps - all are excellent, but AutoSleep is the one for me after testing them all and the native watchOS only solution.
You can manually activate Sleep on your Apple Watch or on iPhone in Health app.
Set up Sleep on Apple Watch
- Open the Sleep app on your Apple Watch.
- Follow the onscreen instructions.
You can also open the Health app on iPhone, tap Browse, tap Sleep, then tap Get Started (under Set Up Sleep).
Note : Your Apple Watch will track your sleep based on the sleep schedule you create or when you manually turn on Sleep Focus. In order to receive sleep data from the Apple Watch, it must track your sleep for at least 4h each night / each time you sleep.
If you are looking for an automatic tracking without a set schedule, check out the free Sleep++ app
It is about as accurate as you'd expect an algorithm to be at guessing when you slept (a.k.a sometimes/often wrong) but I like it for weekend sleep tracking because I don't set a schedule for the weekends.