I don't use them.   If a dog or cat can get in them then so can a
small  child.   And since that small child may very well be carrying
a gun and just as soon kill you for whatever I would not use
a cat/dog door.

my sister installed one for her cat.  The electronic part of it will only
open if the cat wearing the collar comes near it.  Her problem with it was
the cat was free to enter the house at will, caring what ever he wanted with
him, so half dead (or not quite so half dead) birds, squirrels and chipmunks
came in with him to play with.  One problem I always had with it was that
the collar was huge, and expensive to replace if he lost it, or worse, could
all too easily get caught and possibly choke the cat.

I had one that only opened when the cat was wearing a magnetic collar.  The
magnetic bit to go on the collar was around $12NZ as I recall so not too
expensive.  Unfortunately when I shifted I lost the mechanism and it's about
$100 to replace.

When the cats go through it you can hear a high pitched whistle as the
locking mechanism is released which some cats take a while to get used to.
It took one of our moggies about a month to adjust to it.

There is no way a small child could get through the cat door unless they
were a baby and babies don't carry guns.  Dog doors might be a different
story.