How secure is an offline android phone?
Some background. I want to use an app called Bither on android, which allows me to create a cold wallet on 1 phone and a hot wallet on another phone.
Cold wallet is a wallet which is created on a computer which never connects to the outside world.
Hot wallet is a wallet which is created on a computer which does connect to the outside world.
Assuming that I keep the offline phone in a secure safe, switched off, and only take it out of the safe and switch it on when I want to sign a transaction.
Even if I remove the sim card, is it possible for someone to get access to the data in the offline phone without physically having access to the phone, even if the phone is switched off and the battery is removed?