I have a Garmin fitness watch that only vibrates to wake me up. It’s mildly annoying since it is not as gentle as my old Apple Watch from many years ago. The Apple Watch’s vibration alarm felt like a finger gently tapping my wrist. It was a nice way to gently wake up without disturbing my partner. My Garmin watch vibrates entirely on the lowest setting. I can also hear it audibly vibrate, too.

Edit: fixed typos from mobile keyboard typing