On the Wear OS platform and ONE UI Watch (Galaxy Watch 4 + 5), we use gentle vibrations for an even more natural wake up. It starts with a single vibration, another in 30s, then again in 20s and so on. After a few minutes, the vibrations become continuous.
This is a companion discussion topic for the original entry at https://sleep.urbandroid.org/docs/faqs/one_vibe.html