[AdmiralBeotch]

I have been doing offline transaction in bitcoin for years now. Private keys on the offline system sign unsigned transactions from an online computer and the interaction is completely over an airgap (webcams and qr codes on/from either side).

Electrum is primarily what I use to do this, but there is an android app called Bither that does essentially the same thing.

Additionally, the Electrum 2.4 client has multi-sig features and it is very easy to setup and use so the security of your funds is distributed across multiple devices/co-signers.