on 06/06/2019, Davidm supposed :
Out of curiosity - what happens if you're not in the garage, the power
fails with the door closed, and you have no other entrance into the
garage?

If the door roll is on the inside, they offer a linkage down and
through an access hole for a manual winder. If the roll is mounted
outside, or there is alternate access, you can just hook an handle on
to the end of the drive for the roll.