An ADHD brain in sleep inertia suppresses up to 94% of repetitive auditory input. That's why phone alarms, Sonic Booms, and bed shakers all fail — sound travels through air, hits the auditory cortex, and gets deleted.
Vibration on the wrist travels through skin and bone to a completely different part of the brain. One the sleeping brain has no way to filter.
That's why your hand on their shoulder works. The Wake Band delivers it without you in the room.