Forgotten PIN on Mycelium Android Wallet: Seed Phrase Failed to Restore Bitcoin
IndeterminateWallet passphrase was unavailable — whether access was ultimately recovered is not known.
In May 2019, a BitcoinTalk user reported a custody failure affecting their friend's self-custody Bitcoin holdings. The friend had created a Mycelium wallet on an Android device, properly recorded the 12-word seed phrase on paper, secured the wallet with a 6-digit PIN, and successfully received Bitcoin into the wallet. When the friend forgot the PIN code, recovery attempts failed in unexpected ways. The friend and user tried to create a backup on the original device, but this action required the forgotten PIN—creating an immediate access barrier. They then attempted restoration on a new Android device using only the documented 12-word recovery phrase. The new device wallet appeared empty despite the seed being correct, contradicting the user's expectation that Mycelium's HD (Hierarchical Deterministic) wallet technology would regenerate the same wallet from the seed alone.
Forum expert HCP clarified that HD wallets always regenerate identical address chains from a given seed, regardless of backup timing. This meant either the recorded 12-word phrase was not the original wallet's true seed, or transcription error had corrupted the recovery words. Expert bob123 noted that Mycelium stores the PIN in unencrypted text on the device filesystem, suggesting that rooting the original Android device or accessing it via Android Debug Bridge (ADB) in debug mode might allow PIN extraction and wallet unlocking—but this path remained untested in the reported thread.
The thread concluded without disclosure of the Bitcoin amount, final outcome, or whether recovery was ultimately achieved. The incident demonstrates a critical operational gap in solo self-custody: the PIN was a single point of failure held only in memory, with no redundant recovery path documented.
| Stress condition | Passphrase unavailable |
| Custody system | Software wallet |
| Outcome | Indeterminate |
| Documentation | Partial |
| Year observed | 2019 |
Why passphrases fail years after they are set
The failure mode documented consistently across observed cases is temporal: the passphrase is set with confidence, not used for an extended period, and then cannot be reproduced exactly when needed. A single character difference — different capitalization, an added space, a slightly different special character — produces a different wallet with a zero balance. The holder may be certain they remember the passphrase while being unable to produce the exact string that was originally set.
What makes this particularly difficult is that there is no signal at the moment of failure. A wrong passphrase does not produce an error message. It opens an empty wallet. The holder sees a zero balance and typically concludes the passphrase was wrong — but without knowing which part was wrong, or by how much.
Professional passphrase recovery services can attempt permutations when the holder has partial information: they remember the general structure, typical patterns they use for passwords, the approximate length, or that it included a specific word. Recovery from total non-recollection is not feasible.
The preventive action is to store a passphrase record — not with the seed phrase, which would defeat its security purpose, but in a separate secure location accessible to the holder and potentially a designated recovery person. A passphrase that exists only in memory has a time horizon: it will eventually be forgotten, and the timing is unpredictable.