If you have small amounts of crypto currency and want a secure machine and don’t want to buy a hardware wallet:

You can take your old phone or tablet, apply any available upgrades, factory reset it, use it only for crypto currency stuff.

Our mobile operating sysmtems are pretty secure (in the grand scheme of things)

You can, but you shouldn't. What if you lose your mobile phone...?

> Our mobile operating sysmtems are pretty secure (in the grand scheme of things)

Not yet. Maybe after Android One / Project Treble runs on the majority of smartphones in the world. Which won't happen since Google made Android Go for low-end devices.

That's three problems. Security of the device(s), the lack of redundancy, and the physical security of the device.

A hardware wallet (such as Trezor or Ledger Nano S) together with a smartphone (or PC) yields you 2FA. "(Or PC)" could mean an offline Linux distribution on a USB key which is used as backup. The hardware key suggests a paper backup which should be safely stored at a notary or safety deposit box. Same for the USB key with the backup Linux distribution. Though it can also just contain some config files (stored encrypted).

Such a hardware key costs <= 100 USD/EUR (plus the costs of the notary or safety deposit box) so for any amount of cryptocurrency _above_ the cost of that it is worth it.

These costs are peanuts for the average BTC user, but for people in poorer countries its sadly quite an investment. Worth it though.

Until you lose it or drop it in a lake or it doesn't boot one day or the flash memory corrupts.

All these people recommending phones or hardware wallets as being easy, and not mentioning the complexity and opsec of offsite backup....

Hardware wallets come with a passphrase mnemonic that completely restores them. Write it down, put it in a safe deposit box, you're done. You can then take an acetylene torch to your hardware wallet, buy a new one, restore from the passphrase, and have everything back. Hardware wallets are far easier to back up offsite than key management on a computer, though a SmartCard-HSM comes close. (Hardware wallets are the same principle as an HSM.)

Since you're probably wondering, the passphrase mnemonic on my Ledger is a group of 24 words that represent a translation of the primary secret key. All accounts on my Ledger are derived from it. I've tested wiping and restoring, and the passphrase now lives in my bank deposit box.

By the nature of cryptocurrency, if you had all the public keys from your hardware wallet you could use it as a bank by dropping the wallet itself in a safe deposit box. You don't need it in your physical possession to receive, only send. I'm considering buying a second for exactly this purpose, though at that point, a paper wallet would be just as functional.

Or, just buy a Ledger Nano S, which handles all of that for you. For serious crypto one uses hardware keys, and cryptocurrency is no different.

s/Ledger Nano S/Trezor

Both work just fine, when compared to DIY. Playing favorites is not how to advocate to people not in the know; I happen to have a Ledger, so it's what I typed.