Re: Still looking for an electronic lock...
I think that would violate building codes in most places. There is, after all, a reason that all the commercially available ones fail open.
The requirement is that people can get out, not that the door unlocks - there's a difference.
I have a flat in a block of four, with a door intercom and entry system. It has a striker plate like the one I posted a link to, and the flap on that is unlocked by the entry system to allow the door to be opened to visitors.
Occupiers can use a key from the outside to retract the latch bolt, or from the inside use the thumb turn to do it.
So the door can be released by releasing the striker plate, or by retracting the latch bolt manually - the latter not being affected by the striker plate failing locked.