I don't personally have a cat door/cat flap - I live in an apartment - and don't really know much about them. I would try a couple things, though:
I would do a search on this site for articles/posts about cat doors.I would try a search on the internet if you can identify the brand of cat door...
Hi, snowpawprint and welcome! I'm new here too, but this site and these ppl and their kitties feel like home to me! I think Egyptian Mau cats are beautiful. I don't know much myself about cat intruders. What kind of area do you live in? Are the intruders getting into your home? Hiding in your...