DIY BTC Wallet for smartphone possible?

[Harchive]

I just got a brand new phone and I still have the old one which I really don't have any use for, one phone is always more than enough for me, so I was thinking about Bitcoin some minutes ago and something comes to my mind, I read somewhere about how people can use DIY Bitcoin wallet on PC, I mean dedicating a old PC or laptop for Bitcoin wallet only, so I thought to myself why can't I do the same on my second phone?

Is there no separate reliable secured OS that cab turn my old smartphone into a Bitcoin wallet only? Like something made for cold storaging Bitcoin, no Internet surfing and no connection to Bluetooth or something, I don't know.

Can anyone help me out? 

[OmegaStarScream]

I wouldn't really worry much about about changing the operating system if you're not going to be use it online anyway. Not sure what you mean by "DIY" though? you want to build the wallet yourself? An open source wallet like Electrum, Bluewallet or Unstoppable (if interested in multicoin) would do just fine.

[Mia Chloe]

~snip

A majority of Android phones today, although android is open source still require you to access internet the very first time you are setting up the device. Considering this particular constraint I'll say you can't safely call it air gapped.

However you can actually format the device after that first connection and never make any connection to the internet. Then you can proceed to root the phone so you have full control (and probably install Linux though not necessary).

However ,a little manual button tap to toggle on WiFi and connect to the internet or even cellular or Bluetooth will make it ineligible as an air gapped wallet once again.

[Charles-Tim]

Mobiles phones can not be airgapped. The WiFi can not be removed and the internet connection will require phone repairer or Engineer to remove it for you and this might not let the phone to boot. You can talk to phone repairer or Engineer about it.

But you can disable the WiFi, mobile data, Bluetooth, NFC and other things that can be used to connect, this may help you but the phone is not airgapped, but safer than it to be online.

[Merit.s]

Since you no longer want to use the old phone, you can just restore it back to factory settings and disable wifi mobile data Bluetooth, NFC . Better you should put it on airplane mode to avoid any connection unknown to you. There's a guide that can put you through but I haven't tried it because I have electrum cold  storage already on a PC.

https://www.webopedia.com/crypto/learn/old-phone-hardware-wallet/#:~:text=Prepare%20your%20old%20phone%20by,%2C%20backups%2C%20and%20safe%20storage

[dzungmobile]

I wouldn't really worry much about about changing the operating system if you're not going to be use it online anyway. Not sure what you mean by "DIY" though? you want to build the wallet yourself? An open source wallet like Electrum, Bluewallet or Unstoppable (if interested in multicoin) would do just fine.

They are good wallets as they are non-custodial and open-source so that they are recommended by many experts.

What are best Bitcoin wallets?
Recommended Bitcoin wallets.

[The Cryptovator]

I just got a brand new phone and I still have the old one which I really don't have any use for, one phone is always more than enough for me, so I was thinking about Bitcoin some minutes ago and something comes to my mind, I read somewhere about how people can use DIY Bitcoin wallet on PC, I mean dedicating a old PC or laptop for Bitcoin wallet only, so I thought to myself why can't I do the same on my second phone?

You can definitely use it for a software wallet. But at the end of the day, you have to connect your wallet with the internet. And there are still chances to drain your wallet if your seed is compromised. So the main thing is securing your seed phrase. I have been using one of my mobile devices as a local wallet. It's just like for local deals, such as receiving funds from clients, receiving rewards from signatures, etc. The smartphone just stays at home; I don't carry that with me. And one phone is always enough for me to carry with me. So I thought, why should I leave it lazy? Just use it as a wallet for local deals.

For holding, I always use my hardware wallet, so if you have a big amount that needs to be held, then it's better to purchase a hardware wallet. As a local wallet, you can use your old smartphone as I described above but make sure it's true noncustodial. Don't leave it lazy unless you need to sell it.

[macson]

Just reset your phone, then install an app like Bluewallet on it. Then, transfer your Bitcoin to that wallet. After that, simply turn off your data plan or Wi-Fi on the device, then turn off, and store your phone somewhere you feel safe. If you don't have a lot of Bitcoin, it should be safe to store it this way. However, if you have a lot, I recommend using a hardware wallet.

[dzungmobile]

However, if you have a lot, I recommend using a hardware wallet.

Hardware wallets are cold wallets which are safest wallets to use if people are ready to spend money for hardware wallets.

There are some notes as like other wallets, choose open-source ones to use. In addition, make sure you buy hardware wallets with recommended advice below.
[LIST] Open Source Hardware Wallets.
[GUIDE] How to buy a Hardware Wallet the right way.

[Harchive]

I wouldn't really worry much about about changing the operating system if you're not going to be use it online anyway. Not sure what you mean by "DIY" though? you want to build the wallet yourself? An open source wallet like Electrum, Bluewallet or Unstoppable (if interested in multicoin) would do just fine.

So all got to do is download a open source wallet, got it, and never connect it online again until I am ready to move my coins to an exchange?

Won't there be need to upgrade the wallet let's say I choose Unstoppable, can old software wallet not become a problem for security reasons because they are older?

[dzungmobile]

I read somewhere about how people can use DIY Bitcoin wallet on PC, I mean dedicating a old PC or laptop for Bitcoin wallet only, so I thought to myself why can't I do the same on my second phone?

You can do anything but must remember to make your wallet back ups. You should never try to do anything cool but skip or forget about wallet backups.
How to back up a seed phrase?

It's not bad if you want to do anything with your old phone but make sure to remember that it is an old device with more risk of technical problems. You must consider your old phone as your backups, or as a hot wallet with very small fund.

It's very dangerous if you store your big fund in a wallet on an old phone that can technically be broken anytime.

[melinoe]

If you don't have that much and you do think that this old device won't stop working one good lucky day -then, yeah, you can reset it and use it as a frankenstein of sorts - to make it as a wallet of yours with no Internet to it, but, as it was said, to fully remove this option wouldn't be possible without outer help.

Or you can just buy a hardware wallet for such operations (as it was outlined). The choice is yours. Risks would be in each of the ways.

[kriminall]

After completely resetting your old phone, you can reinstall it and then download a wallet that supports offline transactions. Perhaps BlueWallet or AirGap Vault. Electrum is also an option, but remember that even if you have an offline wallet, you need to sign the transfer on an online device to process the transaction. If you have a large amount of money, the Pixel + GraphenOS combo is also worth considering.

[arabspaceship123]

I just got a brand new phone and I still have the old one which I really don't have any use for, one phone is always more than enough for me, so I was thinking about Bitcoin some minutes ago and something comes to my mind, I read somewhere about how people can use DIY Bitcoin wallet on PC, I mean dedicating a old PC or laptop for Bitcoin wallet only, so I thought to myself why can't I do the same on my second phone?

Is there no separate reliable secured OS that cab turn my old smartphone into a Bitcoin wallet only? Like something made for cold storaging Bitcoin, no Internet surfing and no connection to Bluetooth or something, I don't know.

Can anyone help me out?  

No OS to make smart phones Bitcoin wallets. You have choices if you want a wallet on your old phone like Bluewallet with wifi. Switch off to keep the wallet offline switch on if you want to use the wallet. If you want to secure Bitcoin you must use a safe wallet, you should give up on making a wallet on dedicated phones. What is a DIY wallet?

[Z390]

I am sorry if I sound harsh, I need to apologise first because people like taking shit too serious on here, if Bitcoin wallet matters this very much to you, why not get a hardware wallet instead of buying that new phone? Since the old phone still works very well I guess this is why you want to turn that into a secured Bitcoin wallet?
I would have leave a new phone and get a hardware wallet like Trezor, two versions of Trezor costs less than a brand new phone, although I don't know which type of phone you got, the problem I have with smartphones is they are always online, makes them not as secured as we think.
Airgapped wallet are the best of the best, they are by far more secured that every other crypto wallets I know, they have better grade security systems in them, for example Keystone 3.

[satscraper]

I just got a brand new phone and I still have the old one which I really don't have any use for, one phone is always more than enough for me, so I was thinking about Bitcoin some minutes ago and something comes to my mind, I read somewhere about how people can use DIY Bitcoin wallet on PC, I mean dedicating a old PC or laptop for Bitcoin wallet only, so I thought to myself why can't I do the same on my second phone?

Is there no separate reliable secured OS that cab turn my old smartphone into a Bitcoin wallet only? Like something made for cold storaging Bitcoin, no Internet surfing and no connection to Bluetooth or something, I don't know.

Can anyone help me out? 

I don't know any reliable OS specifically centred on Bitcoin but If your phone is Android-specific, you might want to try running it in single-app kiosk mode and installing AirGap Vault. This could turn your device into a secure vault, with security comparable to that of the best hardware wallets.

Also ypu can try installing LeanageOS which is open source on your old Android phone and run AirCap Vault.

[joniboini]

Also ypu can try installing LeanageOS which is open source on your old Android phone and run AirCap Vault.

Maybe you mean LineageOS? It's been so long since I've heard that name again. I've never modded my phone since a few years ago, but I've been downloading and installing custom ROMs many times in the past. Is his old phone is supported is a question OP needs to answer before he does this, if my memory serves me right. CMIIW.

[coinlary]

You already have a  PC that does the work for you , there’s  no need of stressing your  self with setting up a nother cold storage on your phone imo.. but if it's  just for the sake of learning and adding up to your knowledge  then why not.

A suggestion  I would give you is just using the phone for setting  up your watch only wallets if  you  don't  know what else to use it for. Atleast, you can get rid of anything wallet on that your  new phone if all you want is just to check balance  from time to time and you can also have a small balance on some wallets setted up on the phone apart from the  watch  only wallet, where you can easily carryout transactions .. Overall  you will  reduce the activities  you will be using the phone to carry out.

[X-ray]

Just factory reset, install non custodial wallet and disconnect it forever from internet, bluetooth, or any interface?

I think i've done this before I owned hardware wallet. It's very easy and your only concern is to back up the seed phrase outside of the phone. So if your phone somehow broken you don't lose your access.

[satscraper]

Also ypu can try installing LeanageOS which is open source on your old Android phone and run AirCap Vault.

Maybe you mean LineageOS? It's been so long since I've heard that name again. I've never modded my phone since a few years ago, but I've been downloading and installing custom ROMs many times in the past. Is his old phone is supported is a question OP needs to answer before he does this, if my memory serves me right. CMIIW.

You're correct, it's LineageOS, I just made the typos on my part. Regarding supported devices, OP can check if their device is on the supported list here. It's also important to note that "Builds for other devices cannot be used." LineageOS may not be compatible with even the same model from a different manufacturing year, so the OP should be very cautious if they decide to proceed with this OS.