See...
Keyed Disconnect Device - Emergency Release
I don't know of any code that would prohibit a vault style (no other entrance) garage, but I always recommend one of these if it has an opener. That's assuming it doesn't already have one...most do around here. Bad enough losing your power, but to then not be able to drive anywhere would really suck.
In case it's not clear, the cable attaches to the traveller disconnect. You unlock the thing and then pull out the keyed section along with the cable. One sharp tug and...Open Sesame. I put one in for a neighbor once. 15 minutes work at most.
The only caveat is that while they can close the door manually, they may not be able to "relock" the door during that time. That would depend on the type of drive, the traveller and, of course, any other locking mechanism the door might still have that could be made functional again.