When I first read this I thought you were talking about the kind of
cat flap I have, but then I read what you said about the collar.

My cat flap is a hard gray plastic swinging door. Actually, it's two
doors, one inset into the other, that is, the larger is really just a
frame. The larger one has a hole in it almost as big as the small
door. The smaller is just large enough for the cat. When the cat goes
one way, only the small door opens. When the cat goes the other way
both doors open because the small one catches the inside edges of the
larger one (the frame). This is a poor description and I'm sure I have
confused you. I have two and one is destined to be installed in the
outside garage wall, but at the moment is in a box. I can take a pic
of it and e-mail it to you if you like.

The large door has a magnet on the bottom and the frame has a piece of
steel inset so the magnet clamps onto the steel, holding the doors
shut against the wind. Yet the magnet is weak enough that the cat can
shove the door open and go in and out at will.

There is no need for electronic gizmos to keep the other cats in the
area outside. You have to teach your cat how to push on the door to go
in or out. Other cats won't know the secret. I've had this door for
about 20 years and it works great. Low tech, too. And it was cheap.

Unfortunately, I have not seen the like in any store for a long time.
The brand is Staywell. I just googled and found quite a selection of
Staywell cat flaps, but none that look at all like mine. In fact, I
didn't find any with this "door inside a door" design. They probably
stopped making it because it worked too well and didn't cost enough.

--
Bogus e-mail address, but I read this newsgroup regularly, so reply here.

We bought one of those $185 wonders and now I wonder why we bought it!!  At
first we could not get it to open soon enough (dogs chased the kids but the
dogs would not enter the house), so the cats would have to make a trip up
the tree in the back yard.  Then the kids would loose the keys after lengthy
discussions with the manufacturer about how to "tune" the flap so it would
open sooner.

We now have the mose expensive "normal" cat door in town.  No more 'keys' to
open it - just open all the time.

BTW - it is a Radio Systems Pet Safe door.  POC in my books.