I am wondering about hardware keyrings like Yubikeys : From a security point of view is it safe to cross international borders with them ? How do you connect back to your accounts without one when all your devices are based on two-factor authentication if your hardware keyring has been seized when by customs. Could you be detained for not "remembering" the second factor to unlock the keyring ?
You could definitely be denied entry and most likely you would be. In terms of detainment, probably only temporarily until they put you on the plane back. Unless they have serious suspicion of something like terrorism they can't just hold you indefinitely for not cooperating.
Ps IANAL. So take this with a gain of salt but I've never heard of someone actually being jailed for not giving access.
This might be the first semi-plausible consumer use case for smart cards as a second factor. One could, reasonably, conceal a smart card as a health insurance (EHIC) or debit card and pass otherwise adversarial border controls with them.
This, of course, is a rather fictitious scenario.