Take a look at OpenDime [1] + ColdPower [2]. First is a one-time hardware private key, with physical protection of it (i.e. you need to break the device psychi

Take a look at OpenDime [1] + ColdPower [2]. First is a one-time hardware private key, with physical protection of it (i.e. you need to break the device psychically to extract bitcoins), and ability to verify address by plugin-in into USB. Second is a USB power from 9-volt battery. So you can check that the OpenDime is active. The only hard part is verifying the balance you need an access to blockchain network. Not necessary to do that through internet, because you can receive it though satellite now [3], but you still need a computer, that's the fact. 1. https://opendime.com/ https://opendime.com/ 2. https://usbcoldpower.com/ https://usbcoldpower.com/ 3. https://blockstream.com/satellite/ https://blockstream.com/satellite/