The above is the Huawei gt2 42mm sport
If you wear your watch at night, you will likely be woken up by a vibration on your wrist. If you don't wear your watch, your cell phone will ring as you are used to from an alarm clock.
And that wakes up too? Or should I always set a parallel alarm clock on my cell phone?
Unfortunately I don't have a smartwatch. But I assume that such a smartwatch vibrates strong enough to wake you up. As long as you don't have the deepest sleep, the vibration will definitely suffice.