In article ,
Bob Eager writes:
On Mon, 02 Apr 2018 15:04:54 +0100, Brian Reay wrote:

They tell me you can get flaps which are coded to the
microchips that each cat has.

You can - but the company was, in the past, associated with an individual
on another newsgroup whom I would not trust. That has probably changed.
The showstopper for me was that it only controlled inward movement, and I
needed per-cat control in both directions. They assured me there would be
an accessory for that, but were unable to tell me how long it would be
before it was available.

I see that Pet Mate do a microchip 4 way version now, though, and they
are a reliable company. They also do one that works with a small ID disc
you put on the collar (not a magnet). Pet Mate have always been good for
support and spare parts, too.

http://www.pet-mate.com/gb

I had a cat when I was a teenager, long before id chips.
I tried building a lock to stop other cats coming in.
Used a reed switch to be triggered by a magnet on the collar.
Problem was the cat would come back in with a necklace of
scrap ironmongary hanging from the magnet collected from the
local neighbourhood. Gave up on the idea.

BTW, always liked the following project:

https://web.archive.org/web/20081014...lo_control.htm

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]