Trezor

Launched in 2014 by the Czech firm SatoshiLabs in Prague, founded by Marek "Slush" Palatinus — the man behind the world's first bitcoin mining pool — and Pavol Rusnák. The Trezor One was the first of its kind: the private key is generated and stored on the device, and transactions are signed on it so the key never touches an internet-connected computer. Both the firmware and the hardware design are open source, which sets it apart from arch-rival Ledger.

Protection rests on a PIN and a seed phrase you write down on paper. Lose both and the money is gone with no appeal — which is exactly the point, and the danger, at once.