We're really talking about access to accounts (e.g. gmail), not the devices themselves (or the former is of more interest, anyway). What's to stop these agents

We're really talking about access to accounts (e.g. gmail), not the devices themselves (or the former is of more interest, anyway). What's to stop these agents from simply demanding you turn over your email/facebook/whatever credentials, regardless of whether you're carrying electronics on your person? IIRC they're actually already demanding Facebook credentials from certain travelers. Unless you literally have no internet accounts, or what you do use is obscure enough to give you plausible deniability, it seems like you're fucked either way.