My father was adamant that no such back-up system was needed or desired.
He was very pleased with how well it worked when my brother and I had it installed anyway. Of course we were very fortunate that it worked so well. If it didn't, we would never have heard the last of it.
Cheerily, Charley Noble, who has no back-up system whatsoever where he lives unless sharing the house with two longhaired cats counts