This was the first thing that came up in a search. Looks like there's a few sizes too:
https://meowspace.biz/product/meowspace-microchip-system/
It looks pretty pricey, but considering microchip pet doors on their own cost about that much, this seems like a cheaper option than DIYing some contraption involving a microchip pet door.
Look around for this kind of stuff OP! It exists!
This was the first thing that came up in a search. Looks like there's a few sizes too:
https://meowspace.biz/product/meowspace-microchip-system/
It looks pretty pricey, but considering microchip pet doors on their own cost about that much, this seems like a cheaper option than DIYing some contraption involving a microchip pet door.
Look around for this kind of stuff OP! It exists!