Bitcoin has had nLockTime since 2013. It’s an integer field on every transaction that sets a block height (or timestamp) before which the network refuses to relay or include it.
Almost nobody uses it. Which is weird, because it solves a problem most Bitcoiners have: what happens to my coins when I die?
The usual answers are bad. Hand your heir the seed — they lose it, spend it early, or you change your mind. Multisig with family — your family doesn’t get Bitcoin. Custodial inheritance service — you’ve just re-added the company you self-custodied to get away from.
nLockTime gives you a fourth option that doesn’t require trusting anyone except Bitcoin itself.
How it works
You sign a transaction today with nLockTime set to a block ~4 years out. It’s a real signed transaction. The network just won’t accept it until block N is mined.
Four things are baked in when you sign: the inputs (which UTXOs), the output (heir’s address), the fee, and the locktime. None of those change without your private key. You give the signed bytes to your heir, they sit on them, eventually they broadcast.
Why it’s good
Compared to handing your heir the seed: the blast radius is bounded to the amount you committed. They can’t drain other wallets. They can’t move funds before the unlock block. The worst they can do is broadcast the inheritance you signed.
Compared to multisig: nobody coordinates at unlock time. Your heir doesn’t need to call anyone. The Bitcoin network does the enforcement.
Compared to a custodial service: there’s nothing to disappear. If we shut down, the signed transaction still works in Sparrow, Electrum, Bitcoin Core CLI — anything that accepts raw transaction hex. We’ve been mostly the wizard that helped you make it.
What it costs you
Three honest tradeoffs, in order of how much they bite.
The fee is signed in years ahead of broadcast. Mainnet fees might be 10x today’s by 2030. The signed tx says “spend exactly N sats as fee” — that’s the deal. We add an optional anchor output the heir can bump via CPFP, but it’s not magic; sometimes you wait.
Spend a committed UTXO and the plan dies. This is the cancel mechanism — feature and footgun simultaneously. Cold UTXOs and the one footgun is a whole separate post.
Post-quantum is real for long horizons. ECDSA signatures aren’t safe forever. The wizard warns you if your unlock lands past 2030. For 30-year horizons, plan to re-sign every few years.
Try it free
Signet is Bitcoin’s test network. No real money. Free coins from a faucet. The whole Bitheritance flow works there at zero cost: build a plan with a 10-block unlock, wait the ~100 minutes, broadcast as your own heir. End-to-end test before doing anything with real BTC.
Strongly recommended. The first time you do this on mainnet should not be the first time you do it.