BitTool Signer

Hardware wallets cost money and add another device to trust. BitTool Signer's idea is that a spare phone can do the same job if it never connects to anything. The app contains no networking code, and on Android it doesn't even request the Internet permission. It walks you through preparing the phone: Airplane Mode on, Wi-Fi, mobile data and Bluetooth off. Encrypted wallet files are kept out of cloud and computer backups, so the written recovery phrase is your backup.

Using it is a loop of QR codes. You pair the signer once with a watch-only wallet by showing your public keys. When you want to send, the online wallet shows the unsigned transaction as a QR code, you scan it with the signer, check what it's asking for, enter the wallet's password and scan the resulting signature back into the online wallet to broadcast.

The part worth noticing is the review screen. Every request is decoded on the phone into amounts, recipients, contracts and fees, alongside the exact bytes and a fingerprint of the request. It flags things like unlimited token approvals, unknown tokens and message signatures in plain language before you go on, and it understands NFT transfers and marketplace listings on Seaport, LooksRare, Blur and Solana, showing what you give, what you get and who else receives something. Each signature needs that wallet's own password. There's no global unlock or remembered session.

Passwords go through 600,000 rounds of PBKDF2, and wallets are encrypted in two layers of AES-256-GCM, one from your password and one from a key that stays on the phone. The backup flow hides the recovery words until you tap, checks that you wrote them down by asking for missing words, and can split the phrase across three recovery cards where any two restore the wallet. It imports phrases in all ten BIP39 languages.

One recovery phrase covers Bitcoin with Native SegWit, Taproot, Nested SegWit and Legacy addresses, PSBT signing and multisig cosigner keys; Ethereum, BNB Chain, Arbitrum and Base, including EIP-712 typed data; TRON and TRC-20 tokens; and Solana. Because it uses open standards like BC-UR, PSBT and EIP-4527, it pairs for signing with BitTool Wallet and with Sparrow, BlueWallet, Nunchuk, MetaMask, Rabby, imToken, Solflare and others. Some wallets, including Phantom and Trust Wallet, can only watch balances and can't send it requests.

The app is free, and the privacy policy says it collects nothing: no accounts, servers, telemetry, analytics or crash reporting. The iOS source is on GitHub under the MIT license, and the Android source is published there as well. None of that is the same as an independent security audit, and the approach still depends on you keeping that phone offline and the recovery phrase protected. Nobody can restore a lost phrase for you.

It suits someone holding savings in crypto who wants offline signing without buying hardware and is comfortable with a few extra steps per transaction. For small everyday amounts, a regular wallet is less work.