How to Make a Cold Wallet Yourself.
1.Device Preparation
Take an old smartphone and perform a factory reset.
Install one or more cryptocurrency wallets.
Enable airplane mode, remove the SIM card, and never connect this phone to the internet or any mobile network again.
After creating the seed phrase(s), you can turn off the device completely.
2. Creating Seed Phrases and Addresses.
Generate seed phrases and corresponding addresses in the installed wallet(s). Write the addresses down on paper.
If you plan to store multiple cryptocurrencies, generate a separate seed phrase and address for each one.
It's best to prepare multiple seed phrases in advance.
These wallets are intended only for long-term storage, not for daily use.
The addresses you generate have never been online — this is what defines a cold wallet.
3.Monitoring
To check your balance, use:
– a watch-only wallet* (import only the public address), or
– a *block explorer (via any browser)
4. Spending Funds
When you need access to your funds, enter the seed phrase into a hot wallet or another cold wallet.
Transfer the needed amount, and **send the remaining funds to a new address with a new seed phrase**.
That's why it's best to create several seed/address pairs in advance.
Important Warning
Many websites offer so-called "safe" seed phrase generation —
they suggest downloading the site and running it on an air-gapped computer to create a seed that has "never touched the internet".
But the danger is not the internet itself, it’s the generation method.
The problem:
Some generators and scam wallets use a predictable algorithm or a limited entropy range.
Developers could already know all the seed phrases that the generator is capable of producing — even offline.
This vulnerability applies to hot wallets, cold wallets, and even so-called “secure” offline tools.
What to Do?
The only way to ensure true security is to generate the seed phrase manually.
You can create a seed phrase by flipping a coin or a dice (example 1, 2, 3 - is 1 ; 4, 5, 6 - is 0)
1. Download a seed generator onto an offline computer.
2. Flip the coin 256 times.
– Heads = 1
– Tails = 0
3. This gives you 256 bits of entropy.
4. Enter the results into the generator (for each 1, click a cell on the grid; for 0, skip it).
5. Count cells from top to bottom, left to right.
Cell #1 is the top-left corner; cell #256 is the bottom-right.
6. The seed phrase is generated strictly according to the BIP39 standard.
7. You can validate the seed and generate corresponding addresses by importing it into any wallet.
8. Write down the seed phrase on paper, store it in two safe locations, never take photos or store it in the cloud.
My colleagues and I use such seed phrases only once — to withdraw funds and transfer the remainder to a new address with a new seed.
⚠️ And remember: Healthy paranoia in crypto is not a flaw — it’s essential for protecting your assets.