Re: Micro SD cards....
Except they're made of METAL.
Not really a problem if they're in something that is metal or has electronics: an electronic car key, for example.
Except, as is standard spy practice, the spy will never being carrying sensitive information with them because, even if it's encrypted and you don't have the key, the authorities might well consider beating the crap out of you to get it anyway. Meanwhile the mule, who the spy doesn't know and doesn't know the spy has carried whatever is needed through or around screening.