long range RFID reader for a doggy door

I am making a automatic doggy door for my house to mainly keep the cat from going outside. The logistics are the the cat goes into the basement and passes by the doggy door. So I would like it to remain unlocked in normal operation and lock when the cat approaches the door. I have an existing doggy door with flexible flaps and the flap has a magnet at the bottom to aid in closing it. I was thinking of making the latching mechanism a simple electromagnet to provide resistance for the cat to keep him inside. One of my dogs is older and not very strong but can get thru the door. I looked at the PetSafe electronic dog door but the flap is hard plastic and much heavier than the flap I have now and my older one would have trouble getting thru it. Also the Petsafe door looks prone to failure because they use a gear mechanism to keep the door locked all the time.until the pet approaches it. I have built and coded projects with Arduino and Raspberry pi before so I am familiar with the language. My thoughts are to used high frequency active RFID reader and put a key fob on the cat so the door locks when he approaches. Other times the door is unlocked.
I have purchased a NRF24L01 2.4GHz Transceiver Module

But am having trouble finding a low cost 2.4GHz active key fob transmitter for the cat collar. I want top use a long range transmitter because I need to ensure that the cat WILL NOT get out the door and want to have it lock when he is up to 3 feet from the door. Im not stuck onb the transceiver I bought, I just picked it because of its range.

Dogs are clever - just train it to press a button to unlatch the door.

The older one is beyond that, and the younger ones fly thru the door so fast. That is why I cant put the RFID reader on them. The time delay between when it would read their tag and unlocking the door is too big

If you find a long-range RFID module for less than a kilobuck each, please share the information here.
In other words, what you want doesn't exist at a price that most of us would ever want to spend.

I have purchased a NRF24L01 2.4GHz Transceiver Module

I can't see that being any use to you unless you get two and make the equivalent of an active tag with the other.

Normally you would use a UHF RFID system for both long range and reading multiple tags in the same RF field.

The cheapest one I know of is this:-
SparkFun Simultaneous RFID Reader - M6E Nano - SEN-14066 - SparkFun Electronics But note you need an antenna with this.

Why must the cat not go outside?

Perhaps RFID is overkill. You don't have 1000 cats, only 1 of which is not allowed out! So perhaps some researching into simpler remote detection of a passive device would be worthwhile. Something more like the anti-shoplifting detectors you see in shops?

PaulRB:
Why must the cat not go outside?

Perhaps RFID is overkill. You don't have 1000 cats, only 1 of which is not allowed out! So perhaps some researching into simpler remote detection of a passive device would be worthwhile. Something more like the anti-shoplifting detectors you see in shops?

The cat is not an outdoor cat and has never been.
the Anti_shoplifting detector is a good idea. Ill google it, but do you have any keywords that you would use for a search on google or here?

phughes69:
The cat is not an outdoor cat and has never been.

So is surely unlikely to go out, given the chance?

phughes69:
the Anti_shoplifting detector is a good idea. Ill google it, but do you have any keywords that you would use for a search on google or here?

All I get is "RFID" matches, and you have already figured out that's not going to have the necessary range, at any reasonable cost.

I could be wrong, but I thought shop security tag detectors work like metal detectors, but ones that are tuned to detect metal objects that resonate at a particular frequency, that frequency being determined by the length of the coiled copper strip in the tag. Unfortunately, I'm no expert in this stuff!

PaulRB:
Something more like the anti-shoplifting detectors you see in shops?

As I said. If you find something in the price range that most of us would tolerate...

[Here's](How do RFID and RF tags work? - Explain that Stuff an explanation of the different technologies involved.

SteveMann:
[Here's](How do RFID and RF tags work? - Explain that Stuff an explanation of the different technologies involved.

I was thinking more of the "dumb" RF tags rather than RFID tags. They are a simple spiral of copper, with no embedded chip, designed to resonate at a particular frequency. The sensors at shop doors detect them in a similar way to metal detectors.

PaulRB:
I was thinking more of the “dumb” RF tags rather than RFID tags. They are a simple spiral of copper, with no embedded chip, designed to resonate at a particular frequency. The sensors at shop doors detect them in a similar way to metal detectors.

And as SteveMann said,

SteveMann:
If you find something in the price range that most of us would tolerate…

Simple enough, but a bit of non-trivial engineering involved. :cold_sweat: