I installed a cat flap on our door for our cat Pablo, so he can leave the house to socialize with the other outdoor cats in the neighbourhood. We didn't have any problem until one of the other cats (Karel) figured out how to use our cat door. Karel started visiting us quite frequently, mostly for stealing Pablo's food, or sleeping in our bed while we're away from home, but it also happened that he peed on our couch. Pablo is quite frustrated every time Karel enters his territory, but doesn't care enough to scare him away. I tried to scare Karel away by making loud noises, by chasing him, squirting water on him, but nothing worked so far, he still keeps coming back.

I was looking for methods to scare a cat away, but all of the solutions I could find like the infra sound emitting motion detectors and the pheromone sprays or powders would also scare our own cat away.

We talked to Karel's owner, but she is not willing to lock her cat up.

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    You say your neighbor isn't willing to lock her cat up, but if you look at the problem from her side, it's not her problem to solve. Have you considered taking the same tactic toward your own cat and keeping him inside, thereby locking out the current and any future problem cats?
    – Allison C
    Sep 22, 2021 at 17:29
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    'Socialising' to cats mostly means either fighting or breeding; they don't really want to 'see their cat friends', they want to defend their territory.
    – j4nd3r53n
    Sep 23, 2021 at 8:24
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    @j4nd3r53n In our case it's not true, they're all neutered, they're mostly just playing and nose kissing. Sep 23, 2021 at 9:32
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    @C.Koca that's definitely not true everywhere
    – Kat
    Sep 23, 2021 at 15:49
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    You should just keep your cat inside. Cats have no “need” to be outside, do not ”socialize” (they are not people!), and cause a great deal of destruction (killing wildlife, pooping in others’ gardens) and hassle (e.g., wandering into others’ houses 🙄). If the problem is lack of stimulation inside, fix that.
    – Reid
    Sep 23, 2021 at 16:01

6 Answers 6


As your cat Pablo has a chip, he always carries a unique method of identification. I would suggest you swap your current cat flap for one that reads microchips and opens up just for your cat. Yes, they are not exactly cheap, especially if you have a perfectly fine regular flap, but it should pay for itself over time in cat food, cleaning bills and a happier Pablo.

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    As an second option where you need to take time instead of money: make it a puzzle to solve to open the cat flap and teach your cat to do so. I am not sure if another cat can learn by simple looking your cat doing it? My grandparents had a cat who was allowed to go into the food storage to catch mice. It need to pull a rope to open the human door a glimpse and come in. No other cat did so too... Sep 23, 2021 at 5:29
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    Another option qould be a one way flap, only out but not in. So your cat will learn fast the schedule, when you come home, to come with you in Sep 23, 2021 at 5:31
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    @Allerleirauh depending on the OP‘s current model, that may be already possible and just a setting.
    – Stephie
    Sep 23, 2021 at 5:38
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    Our neighbors tried that and it didn't work. The neighbor cats came to the flap, their own cats tried to defend their territory, came to the other side of the flap, and thus unlocked it.
    – Philipp
    Sep 23, 2021 at 8:19
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    Another similar but somewhat cheaper option is to use the type of flap that responds to a magnet on the cat's collar. Assuming the neighbor's cat does not have a magnet. This type doesn't need electricity either.
    – Berend
    Sep 23, 2021 at 12:21

The high-tech version is to use a camera, machine learning, and a solenoid to lock/unlock the catflap. Ben Hamm had a video about a system like that, although his problem was not detecting a particular cat, but to determine if Metric had an unwanted "gift" or not.

Probably this is more expensive than a chip reader, but you learn more by building it.

  • Very interesting answer! But depends hard at the interests of the owner :D Sep 24, 2021 at 3:38
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    This is such a StackExchange answer lmao Sep 24, 2021 at 14:26
  • It would be easier to hire someone to open and close the door for the cat
    – Valorum
    Sep 24, 2021 at 18:41
  • @Valorum That’s how cats see their owners: “servant who opens doors for me”. And tins of tuna. ^.^
    – Stephie
    Sep 25, 2021 at 16:08
  • @Stephie Dogs have owners - cats have staff! Sep 25, 2021 at 19:49

Our friends have a cat flap that is magnetic. Their cats have small magnets on their collars that open the cat flap and also trigger their food dishes (which are covered with a motorized cover).

Of course they always leave the door open anyway and the dogs scare away anything that comes in, but still, the magnets seem to work pretty well.


You could always close up or get rid of the cat flap. Cats can be pretty smart and patient about knowing when they can expect to be able to go in and out, sometimes even meoiwing at a window after hours if needed. They're good at sleeping in the bushes by the door, waking up when someone comes who can let them in. Worst case the poor dear is stuck out all night, but that won't hurt them (not even emotionally).

At first your cat may be terrified, clawing pitifully at the non-working flap, but it won't last long. After a few tries, maybe with you standing outside and the door closed, it will figure out that if it waits, a human will let it in eventually.

Not being able to flee through the cat door to safety might seem dangerous, but if your cat is already going more than 50 feet from your door, it's in the maximum amount of danger (from dogs or coyotes or just cars), flap or not.

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    "Worst case the poor dear is stuck out all night, but that won't hurt them" Well there's plenty of places it would get cold enough outside to hurt them. Sep 24, 2021 at 14:27
  • @AzorAhai-him- If it's not too cold during the day for your cat to frolic outside, it will be fine overnight nestling up in a snowbank in some undergrowth, safe from the wind. My cat would pop right up from below-freezing temps sleeping in the bushes. Sep 24, 2021 at 16:09

If you have a hallway or porch, you could close the next door and make it difficult for cats to open.

That way you can at least limit how far the neighbour's cat can come, and your own cat can still get some shelter until you come around and let it in.


I've trained cats... using water is effective when they have zero training. Eventually you can just use verbal commands tho. Anyhow:

  1. Keep the cat door locked when you're not home until this issue is resolved.
  2. Get a water gun. Every single time you see that neighbor's cat entering or in your home, blast it in the face with water. It'll run back home. Eventually it will learn not to come into your home at all. At that point...
  3. You can leave the door unlocked when you're not home.

That said, I'd expect that cat to try the door again after maybe 1 month. Repeat step #2 then. Then it will probably vanish for say 6-8 months. Repeat step #2 again. At that point it won't happen again.

  • 1
    "it will learn not to come into your home while you're home" FTFY
    – vsz
    Sep 24, 2021 at 22:02
  • @vsz Yes. But it will also assume that you're home when you're not. I doubt it's going to be eager to explore your house to see if you're in there or not. It's more tricky if you were training your own cat because the difference between "don't do this when I'm here" and "never do this at all" is way harder to convey.
    – HenryM
    Sep 24, 2021 at 23:37

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