Your current 12+12 split has a critical flaw: each location is a single point of failure for access. If one burns, you can't recover. The goal should be: any single location failure = no loss.
Simplest fix: Full copies with a passphrase
Store all 24 words in both locations, but add a BIP-39 passphrase (the "25th word"). Now:
Seed words stolen without passphrase → funds safe
One location destroyed → recover from the other
Passphrase stored separately, in your head, or in a third location
Coldcard and some other devices support this. You create e.g. 3 shares where any 2 are sufficient to recover. Store each share in a different location. One location destroyed or stolen → still secure.
This is mathematically sound — not a DIY word split, which offers no real security guarantee.
What I'd actually do
Metal plates (not paper) with full 24 words + a strong passphrase you've memorized. Two or three locations. This is simple, robust, and doesn't require trusting any software implementation of Shamir.
Your current 12+12 split has a critical flaw: each location is a single point of failure for access. If one burns, you can't recover. The goal should be: any single location failure = no loss.
Simplest fix: Full copies with a passphrase
Store all 24 words in both locations, but add a BIP-39 passphrase (the "25th word"). Now:
Cryptographic solution: Shamir's Secret Sharing (SLIP-39)
Coldcard and some other devices support this. You create e.g. 3 shares where any 2 are sufficient to recover. Store each share in a different location. One location destroyed or stolen → still secure.
This is mathematically sound — not a DIY word split, which offers no real security guarantee.
What I'd actually do
Metal plates (not paper) with full 24 words + a strong passphrase you've memorized. Two or three locations. This is simple, robust, and doesn't require trusting any software implementation of Shamir.