I do exactly this. I lined a cookie tin with foil, and tested it by holding the closed box (with the keys inside) next to the car. It didn’t unlock. Then I opened the box, and it did unlock. The box has to be closed (lid fully on, no gaps) or the car will still unlock.

Of course this only foils overnight theft. I imagine it would be trivial for someone to follow me from a car park to a public location and sit next to me to get the key signal from my pocket.

I would imagine the signal emmitted from the fob is time sensitive. The codes should be invalid within a few seconds. If not, shame on them for such a terrible step backwards in security.

Does an unlined cookie tin not work? Does having the lid mostly closed (but with some small gaps) at least cut the effective range?

I’m wondering if a tin facing away from the door may be sufficient since the signal will be reflecting in the wrong direction.

Then just a metallized flap for extra protection.

Leakage is fine. As long as it’s in the right direction.

I didn’t test rigorously but an unlined tin did not block the signal when the tin was right next to the car. Maybe it still reduces the range.

I've watched some DIY videos and am considering doing just this. I'm not sure how tight a seal you need though (one video said you want overlap from lid to sides/bottom), and the draws we have there aren't super tight. Maybe we'd make an enclosure within the drawer and be able to line that sufficiently?

If anyone knows how much leakage there would be for fobs/phones, and whether it makes a difference for this application (where the sniffer/attacker would be 10+ feet away), I'd love to know it!

Would be easy to test what is needed. Wrap up your keys and take them to the vehicle.

I just completely wrapped my remote with one layer of aluminum foil and that was enough. A small gap on side was enough for the car to detect it.