@feld Yes, if an attacker has physical access to your computer, you are screwed no matter what - there is no way around this sad reality.

If you use full disk encryption and the computer is shut down, the attacker won't be able to access any of your data - although if the attacker decides to clone the storage and attaches a keylogger/recording device and you don't notice, the attacker will be able to get your password and use that to extract the cloned storage.