Mike, there’s a lot of hoo-ha about Faraday boxes and cages. All that’s needed to block the signal from a key is something made of conductive metal with any gaps smaller than the signal’s wavelength. So any fully enclosed metal box will do. In fact wrapping the key in aluminium foil will do. We have an old pewter box with a lift up lid on the hall table and our keys live in there. Hope that helps.