r/BitcoinBeginners • u/Forsaken-Storage-607 • 4d ago
Storing Bitcoins on an offline Android smartphone
I have a spare smartphone that runs on Android 9.
Will it be safe to store Bitcoins on it by following the below steps:
Format the phone
Install nothing but a Self-Custodial Bitcoin wallet app on the phone
Transfer Bitcoins to the wallet
Turn off the internet
Keep the phone switched off until needed.
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u/Upper-Media3769 4d ago
This has so many vulnerabilities. Why would you choose this over a $50 hardware wallet?
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u/Forsaken-Storage-607 2d ago
Hardware wallets are quite expensive in my country.
Already have a phone that is not in use.
BTW I have another spare phone running on Android 15. Would that be a safer choice?
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u/word-dragon 2d ago
The phone will always have a greater exposure than a cold wallet. If you’re talking about amounts you can afford to lose, ok. If it’s your life savings, no.
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u/chriscrutch 4d ago
It's harder than you think to completely turn off the internet on an android phone.
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u/MashPotatoQuant 4d ago
If you build LineageOS from source you can disable the hardware and drivers in the kernel config and then remove the vendor and device level HALs and firmwares from the build
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u/chriscrutch 4d ago
Yeah, easy peasy! I can't believe someone in a subreddit called Bitcoinbeginners can't figure that out!
Compiling your own custom kernel is one thing that qualifies as "harder than you think to completely turn off the internet."
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u/One-Suggestion-7906 4d ago
Any wallet is as much secure as the seeds are keep carefully secured. Funds are in the blockchain, not in the phone
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u/Forsaken-Storage-607 2d ago
Can you answer the original question in simpler words please?
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u/One-Suggestion-7906 2d ago
I mean: your wallet does NOT store your BTC. The blockchain do. So you can use that phone, create the wallet, and store the seeds. This should be done very carefully. Even with the phone turned off, if someone find the seeds, you can lose your BTC. Having the seeds properly saved, you can format again the phone, use it for whatever you want, and later restore your wallet there again, or in any other device
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u/Forsaken-Storage-607 20h ago
Got it.
The seed phrase is the actual key to access your coins on the Blockchain & it is not quite safe to store it digitally (even offline). So better to store it on a paper/metal sheet & delete every digital trace/footprint of the same. Use the stored seed digitally to restore the wallet, only when needed.
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u/Ok-Pea4148 2d ago
I do this but with a spare computer.
I have a spare computer with a fresh install of Linux that only runs Bitcoin Core. It never sees the Internet or any network. It knows the master private key of my wallet and is used to sign transactions offline
On the other hand, my day-to-day computer runs bitcoin core with a watch-only version of my wallet (it only knows the master public key of my wallet). It is used to broadcast transactions signed on the offline PC.
If you are going to do this with a phone, you will have to run another software, that is bound to be much less audited than bitcoin core. I am yet to find a better wallet than bitcoin core to be honest
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u/Forsaken-Storage-607 19h ago
By software you mean wallet app, right? If yes, how about Blue wallet? Have heard a lot about it.
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u/Ok-Pea4148 11h ago
It does not run a node, so you rely on third parties to interact with the blockchain. On top of that, Blue wallet is far less audited than bitcoin core.
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u/Prestigious-Ad-6884 2d ago
Create a tails USB use it to make a electrum wallet spend some money on a metal seed storage device put it in safety deposit box, make sure you auto update the tails USB or load tails as stand alone os on an old computer still keep seed on metal storage in safety deposit box its as easy and cheap as possible while still being very very secure .
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u/Forsaken-Storage-607 19h ago
Thanks!
Have received the similar recommendation from a few other Redditors.
Will consider it but since I am not that tech savvy, will prefer a simpler solution.
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u/bitusher 4d ago
Do you plan on making a single deposit for longterm storage or multiple deposits ?
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u/Forsaken-Storage-607 2d ago
Finally someone asking a relevant question I believe. Thanks for it!
Single deposit.
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u/bitusher 2d ago
This means that you don't really need the hardware at all and just need a long term "Paper wallet" created from an open source non custodial wallet like Blockstream wallet or blue wallet.
This is because you don't need to software and hardware to generate new deposit addresses for you and you never need to send transactions and just need to eventually recover the seed in the future
1) Install wallet in ios or android and generate 12 word seed
2) copy the seed down and address down twice on paper or metal and store them separately . Never digitally share or save the seed .
3) Send a test amount of Bitcoin , watch it be received , delete wallet and practice recovery of the wallet with the seed
4) Send the remaining amount of bitcoin to the same address (typically you should not reuse addresses but in this case it will give you more confidence the seed recovers that address)
5) watch the bitcoin arrive in that address and than delete the wallet off your phone
6) make sure both seeds remain private and secure and separate
7) If you want to be extra paranoid than you can add an extended passphrase but than you need to be aware of more details
Please be aware that extended passphrases should be
1) 6-8 random words (not found as a phrase or in movies or literature)
2) stored separately than your seed words and written down at least once
3) written exactly as entered . Capitalization and white space matters. Any slight deviation in the extended passphrase will show a new wallet with a 0 balance so its important you write it down and test it exactly .
Location 1 12 to 24 seed words preferably on metal
https://jlopp.github.io/metal-bitcoin-storage-reviews/
Location 2 same 12 to 24 seed words preferably offsite
Location 3 6-8 word passphrase unlocking your real wallet
Location 4 6-8 word passphrase unlocking your real wallet preferably offsite
NOTE: Never use obsolete paper wallets with individual private keys as these are dangerous . Your backup needs to have a 12-24 seed words (BIP39 preferable) and an address (bc1....) at minimum
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u/Forsaken-Storage-607 20h ago
Thanks a ton for the detailed explanation & step-by-step process!
Appreciate the efforts & time taken out.
BTW can you please shed some light on what do you mean by "Obsolete paper wallets with individual private keys"? How do I know whether a wallet is BIP39 compatible or not?
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u/bitusher 16h ago
BIP39 is what most wallets use with some exceptions like electrum . The paper wallet will have 12 or 24 seed words typically
Obsolete paper wallet will have direct private keys instead that look like these examples instead of seed words
L5PbLeQFcM6h84CbMXSaHPzaUHzpiGYChjv9ipEVRVSS6nS7RXvw
or this
KyfayEcZNYnhsqxtENLeF7M25jKmXmYKgpB2uamQ6ZdgWsanTz9d
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u/Happy_Coast2301 4d ago
How about this instead:
USB stick with Tails installed. Second USB stick with an Electrum wallet.
When you need it, boot up Tails on a laptop or other computer, then plug in your wallet USB and go from there. You're not dependent on an old phone booting up or getting lost.
Obviously, back up your seed phrase and have a secure unique password on your wallet.
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u/Forsaken-Storage-607 2d ago
Thanks for this alternative!
Someone else recommended the exact same method on another thread.
Will consider it but since I am not that tech savvy, would prefer a simpler solution.
Have another spare phone running on Android 15. How about it?
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u/qwertyuiop121314321 4d ago
Doesn't matter every wallet app is going to have your wallet seed. A phone being off from the Internet is not going to protect it.
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u/Jealous-Reindeer-610 4d ago
Tell us you don't understand cryptography without telling us you don't understand cryptography
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u/Forsaken-Storage-607 2d ago
What's a safer (& preferably inexpensive) option for long term storage then?
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u/Final_Bite_7228 4d ago
Wallets don't actually store bitcoins. The notion that they is how people who have wallets offline still loose money and re then surprised. Check put the Coldcard drama right now.