How can I keep a stray cat out of my house?

I have a cat for whom I keep a window open, since she likes to go outside and come back in while we are gone at work.  Apparently, a neighbor's cat has come in our house to spray.  Does anyone have ideas on how I can keep the cat out?

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Burf7 years ago
If you are looking for some kind of barrier  that will discriminate between your cat and a stray, I'm afraid you are likely out of luck.  Other than a dog that is friendly with your cat but will reject the intruder, I think your only recourse is to trap the stray and turn it over to animal welfare.
frollard Burf7 years ago
There are rfid unlocked pet doors - put chip on pet's collar and they can enter/leave whenever; but intruders find a locked door.  Useful for animals of all types:  rodents, neighbor's pets, deer, and of course, burglars.
Enricommuter (author)  frollard7 years ago
Thanks!  I have considered installing an rfid pet door.  We've had problems keepign a collar on our cat, but I suppose the worst thing that could happen is we lose a collar and the cats stays outside for a day.
If a collar doesn't work and its extra-important, then perhaps a harness is the right trick :D
Enricommuter (author)  Burf7 years ago
Thanks.  I'm considerig trapping it.
seandogue7 years ago
It sounds like you've set up an insecure access point. Consider installing a cat door with "keyed" access. The "key" can either be a fob that hangs from her collar or is a subdural implant.
Enricommuter (author)  seandogue7 years ago
I like the subdural implant idea.  I have asked the Instructables community about a subdural rfid-activated door.  I am just getting to know how to use Instructables, i.e., see replies to my questions.
Thanks for the reply!
Re-design7 years ago
If you can spray the intruder cat with a spray bottle of water a couple of times he will probably stop coming in.  They REALLY hate getting sprayed.
Enricommuter (author)  Re-design7 years ago
Wish I could see it to spray it!
Most do, but not all. One of my girlfriend's cats seems to like it; she had to find other ways to correct him.
That's surprising.  Not that a cat might like getting sprayed but that you have more than one girlfriend!  I thought us geeks were only allowed one per lifetime.  Someone out there must be missing his. 
What can I say -- you've been hanging out with the wrong crowd.