Faraday cage cover for electronic door lock to make the cat flap work

Faraday cage door cover

Copper cover for the door lock, the front is held on with magnets

I realise this is a bit of an odd one, but if you keep reading I can hopefully explain the issue. And if someone else out there is having the same problem hopefully this helps.

Let’s start at the beginning. I had a SureFlap catdoor installed at my house. Those are the ones that read the microchip in the back of your cat’s neck so they only open for your cat. You can program them with up to 32 cats and they are awesome because it means other cats can’t come in your house and pee on all your stuff. Only your own cat can do that.

The 33rd cat

If you are going to program your catflap with 32 cats you should let all the cats in, otherwise it’s just mean

Unfortunately it didn’t work and wouldn’t let my cat in. I spent lots of time trying to figure out why and if it was faulty (which is REALLY difficult when you have a very uncooperative cat). Eventually I realised it was because we had a keypad and swipe card reader for our door and that the reader from that was messing with the reader on the catflap and stopping it from working. So I did some googling and read about faraday cages, EMF (electro magnetic field) and a bunch of tutorials on making wallets and things that would stop people stealing your credit card details. After I had made an aluminium foil hat to stop the government reading my thoughts I set about coming up with a solution for the catflap issue. I found if I put enough aluminium foil around the keycard reader for our door it would block the EMF and the catflap would work.

Explanation of cat flap/door reader issue

So the solution was to make a cover to go over the keypad/swipe lock that would block the EMF but also be easy to open because we need to get inside as well. The prototype was made of cardboard and aluminium foil and was intended to be used for a couple of weeks until I got round to making the proper one. A year later it blew away in a storm so I had to make a more permanent version.

I looked at a quite a few options for the design, but was quite limited in what I could do. I wanted to use copper because it seemed like it would work the best. I had also been keen to use mesh so it would be an actual cage but couldn’t find any that wasn’t really expensive. I have no metal work equipment (or metal work skills) so couldn’t do anything with solid copper. I ended up making the box part from wood and using embossing copper foil to cover it. The embossing foil was from an art supplies store and is thin enough to cut with scissors. I had planned on using a hinge but had trouble finding a spring loaded one so had settled on a hinge with magnets to hold it shut. My husband suggested getting rid of the hinge completely and just using magnets to hold it on. I went with this option as I really like magnets and liked the idea of it snapping into place when you put the cover on.

Faraday cage in progress

Wooden box with magnets glued into the frame to hold the cover in place

One issue I had with this was that when I put the copper over the wood and magnets it made the magnets further apart from each other and lose their strength, so I had to add more than what’s in the picture above. Another thing I found was that it needed the metal to have contact from the lid to the actual box, otherwise it didn’t work.

It’s been up for a few weeks now and is working well. It’s easy to remove the front cover to use the keypad and the magnets have held it in place. And the lovely Mrs Doyle is enjoying the use of her catflap. When she remembers it is there.

I realise that it probably seems crazy to go to this much effort when I probably could’ve had an electrician in to change the unit to one that would work with the catflap. But when you are into craft the allure of making a faraday cage solution will override commonsense every time.