A bit of science..
"By the way, science and radio engineering tells us that if you want to make your own Faraday cage, you want to use a highly conductive metal, like copper or aluminum (but not anodized aluminum). If you use a mesh, make sure the holes are smaller than 1/10 the wavelength of the signal. In North America and Japan, car remotes transmit at 315 megahertz, which is a wavelength of about .95 meters, so a mesh with holes smaller than 9.5 centimeters should work. Other countries use key fobs that work at 433.92 MHz, for a wavelength of .69 meters, so holes under 7cm are what you’re looking for. Those are pretty big holes. In our mesh box they were a lot smaller.
And the one thing you must do when making a Faraday enclosure for your key is to make sure the box closes. Otherwise, the radio signal will get in, and the relay exploit could still work.
Science notwithstanding, our experience tells us your best protection against the relay attack is to line a box with aluminum foil. It’s more reliable, even though a nice mesh box probably works well enough and certainly looks cooler."
https://makezine.com/2015/08/14/block-car-door-relay-hack-faraday-cage/
My first box had a neat plastic insert to hold the key but this insert was suspended by the rim of the lower box, so when the box lid cam down there was a rim of plastic visible. This, surprisingly, allowed the signals to get out and the car door could be opened. Next box had a overlapping lid, so when closed there was no gap. Standing next to the car, key in box, didn't allow me to open the door.