Sweep (Wallet)

To sweep a private key is to broadcast a transaction that sends the entire balance controlled by that key into a fresh address inside your own wallet. After a sweep, the original key holds zero satoshis, so any lingering copy of it — on a paper wallet, a backup, a photograph, or a compromised device — is harmless. Sweeping is the standard way to claim funds from paper wallets, physical bitcoin collectibles, gifted keys, and any key whose history of exposure you cannot fully account for.

Sweep versus import

The distinction matters more than the similar-sounding names suggest. Importing a private key merely adds it to your wallet's keychain: the coins stay at the original address, still spendable by anyone else holding a duplicate of that key, forever. Sweeping moves the value on-chain to a key that only your wallet — ideally one derived from your own seed phrase — has ever known. The rule of thumb for paper wallets and untrusted keys is absolute: always sweep, never import. A paper wallet may have been photographed at generation, printed on a compromised printer, or duplicated before it reached you; importing preserves every one of those risks, while sweeping extinguishes them the moment the transaction confirms. Note the asymmetry in cost: importing is free, sweeping pays a transaction fee — and that fee is the price of actually owning the coins outright.

Mechanics worth knowing

A sweep spends every UTXO the key controls and sends the total, minus fee, onward — there is no change, because nothing is left behind. Wallets typically build this as a send-max transaction. During high-fee periods a sweep of many small UTXOs can cost real money since every input adds weight; if the funds are not at risk, waiting for a quiet fee window is legitimate, but if the key may be exposed, the calculus flips — move first, optimize never. Sweeping is also the standard incident response after a seed phrase or key may have been leaked: sweep everything to a freshly generated wallet on a clean device (ideally backed by a hardware wallet), then investigate at leisure.

Privacy considerations

A careless sweep can undo separation you meant to keep. Combining several swept UTXOs with each other — or worse, with coins from your existing wallet — links them all under the common-input-ownership heuristic, telling every chain observer that one entity controls the lot. Privacy-conscious practice is to sweep each source into a fresh, isolated account, label the resulting coins with coin control, and only merge histories deliberately, if ever. Sweeping to a brand-new address rather than a previously used one is basic hygiene — see address reuse for why destinations should always be fresh.

The sovereignty angle

Sweeping is self-custody's enforcement mechanism. Keys generated by someone else — a paper-wallet service, a collectible's manufacturer, an inheritance envelope — represent trust in every party who ever touched the entropy. A sweep converts that inherited trust into verified ownership: coins under keys you generated, on hardware you control, with a backup only you hold. It is a single transaction that turns "probably mine" into "provably mine," and that is always a fee worth paying.

Consider the common case: a paper wallet from 2014 surfaces in a drawer. The wrong move is typing its key into the first wallet app a search engine suggests — a class of fake apps exists precisely to harvest such keys. The right sequence is unhurried and boring: verify the balance by looking up the address (never the key) on your own node or a privacy-respecting explorer; prepare a destination wallet whose seed you generated and backed up yourself; sweep during a reasonable fee window into a fresh account kept separate from your other coins; and only then, after confirmation, treat the paper as scrap. Ten careful minutes converts a decade of ambient risk — every person who ever saw that drawer — into settled ownership. That is the sweep's real product: not moved coins, but eliminated doubt.