In news:ypdwg.69$6G3.5@trnddc05,
Grandpa typed:
Brian O wrote:

I saw the movie "Over The Hedge". There was a dog that had
a
collar that would activate a doggie door that only a critter
with
the collar, and maybe a critter tagging along with it, could
pass
through, then it would lock again. I haven't seen such a
device. Are there such things? And if so, do they work?
Anyone that has
used these, if you might chime in? Thanks.

It was a cat. But look at this:
http://www.petsafestore.com/stinelpetdog.html
Yes, they work.

Hmm, intersting. It's infrared though; too bad they don't make
one using a radio signal - more reliable less prone to dirt/fur
messing it up.

Any further sources?

Pop`