I have two dogs and two cats. The cats are indoor only and I want the dogs to be able to come and go at will. I've researched online and found electronically keyed very expensive Star Trek style dog doors that are $500+, which is too pricey for me. Does anyone have an alternative or DIY method for achieving this?

  • what size are the dogs and what is the most you would consider for a solution? – allindal Feb 18 '11 at 21:22
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    Years ago, I remember seeing someone had rigged up a camera to their pet door to only allow their cat in when it wasn't carrying something. (something about bringing half-dead mice in). It was probably circa 1999/2000, when I still working on Fark. Unfortunately, I can't find it via Google ... I remember the person had posted pictures of 'things the computer didn't let in', and there was a skunk silhouette. – Joe Feb 21 '11 at 2:46
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    Found it ... quantumpicture.com/Flo_Control/flo_control.htm ... although in your case, the stock electromagnet pet door with the collar would probably would be enough. – Joe Feb 21 '11 at 2:51
  • Teach the dog to pull on a handle that the cat can't reach or isn't heavy enough to activate? – endolith Dec 2 '11 at 19:33
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    @wallyk: meta.diy.stackexchange.com/q/847/22 – Niall C. Aug 24 '13 at 3:04

A search for "electronic dog door" and/or "selective dog door" turns up several products ranging from $80 to $200 (though they are others that go up to $500), depending on size you need, for example:

There's lots of small selective cat doors, they do seem to get much more expensive as you go bigger.

As far as DIY, there are several ways to do this, and the complexity will really depend on exactly what you do, and how much experience you have doing electronics and embedded programming. An instructable on an RFID cat door may get you started.

Effectively, you just need to buy/build the actual door, which is capable of being locked by some mechanism (I would suggest not using one of the flexible flap ones).

Then you need a lock mechanism that can be controlled electronically, such as a solenoid, linear actuator, or servomotor.

Finally, you need the sensor and control circuitry. An Arduino is probably a good staring place for the controller. For the sensor, RFID has a lot of benefits, but as some of the off-the-shelf products show, you could also use infrared and/or magnetic sensors. I would think those would be more finicky to get working reliably, whereas RFID is pretty simple: just mount the antenna so it can pick up the tag attached to the dog's collar when close to the door.

Here's another instructable on interfacing RFID to the Ardunio. All that needs is an output hooked up to the lock mechanism you build, and the software to hold the lock open for a few seconds after detecting a valid RFID tag.

Note that the hardware to do this DIY isn't necessarily cheap, and in fact, probably approaches the $100-200 price tag on some of the off-the-shelf doors. Great learning experience but don't expect to save much cash DIY here.

  • The dogs are about 50lbs, 20 inches at the shoulder. I've seen the two you have listed. One is too small, the other gets terrible reviews. I may look at the RFID solution, but I would prefer a "off the shelf" solution to "rolling my own". – user1797 Feb 23 '11 at 21:57
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    I've had the PetSafe SmartDoor for about 8 months for my Boxer. It works great unless you've got your dog crated right next to the door, like I do. It just keeps locking and unlocking. I also have two cats and they haven't made it through. With that size dog, you'd probably want the large one. – Jeremy White Jul 17 '12 at 17:51

Very interesting problem. It seems to me that if you REALLY want to keep the cats inside (no slip ups, as we would want with our cats) then there is not a simple solution. If the cats get along with the dogs (I am assuming they do), then when the dog with the magnetic collar (or RFID, or whatever) gets near and activates the door, the cat could quickly dart out through the open door/flap.

If you wanted the pet "valve" to work the other way, it would be simple - the dogs are larger, so you can use a smaller door. But the opposite is the trick. Dogs are bigger, but cats can easily stretch up or jump up to a higher door. A weight sensitive mat might let you discriminate between the dogs and cats, but if both cats get on the mat at the same time, that might be enough to trigger the door (depends on how big your cats are). For fifty pound dogs, maybe that is not a worry, but again, the cats could still dash out.

It almost seems you need a dog door with the wiring reversed, so that when the trigger mechanism on the collar comes near the sensor, the door locks. Put the trigger collars on the cats. Then the door allows free entry/exit for the dogs at all times, but if the cats approach it locks. That seems it would work and might only require minimal DIY, a little rewiring of the door mechanism, and maybe not too involved for a simple magnetic sensor door. Hope this helps.

  • +1 for addressing my concern. We tried something similar and the cats would just dart between his legs as the dog went through the door. – Steve Jackson Feb 28 '11 at 14:13

I trained my dog from darting out the front door by placing a spray bottle full of water by the door. Every time I left and the dog was too close, I sprayed just a little water on his face. I placed the water bottle on my porch so that when I got home and he was right at the door, he got a little spray on the face and backed up. It worked perfectly, and I no longer have to carry a spray bottle.

I used this same method on my cat. Now when I open the door to let the dog out, I don't have to chase the cat, and no one gets hurt.


Not that this is necessarily a pet-friendly solution, but perhaps some good old fashioned Operant Conditioning is in order. The trick is to keep the cats away from the door. Perhaps you should rig the cats up to an electronic pet boundary. After a few zaps for getting to close to the door they are bound to become averse to the idea of approaching it.


We have just gotten an indoor kitten and already have an indoor/outdoor dog. The current "doggy door" is inside a cabinet whose doors have been removed. If the product described above was produced, it would answer our problems. The other idea we've had is to create an electronic field around the opening of the cabinet which allows the dog entrance but the cat doesn't have the required tag for entrance. But that seems opposite of how the electronic field would work. ==>If you attach the wires around the outside of the opening of the cabinet, you are keeping things inside that space (including the cat.) Opposite of our goal of allowing the dog in, the cat out....