If I was building a black box to detect hidden data on a USB stick, I'd include a feature whereby it measures power consumption and flags USB drives that don't consume the expected power for that type of drive.
Fucking up every single import and traveler on the off-chance one in seven billion scans detects one of these devices and, further, carries some data the US cares enough about to chase down to this degree?
No. Nope. Nuh uh. Insanely unreasonable. You will get ONE at a station, which you only bother to use if you can convince your $12/hr employee to even give a shit. Literally an insane proposition.
https://www.alibaba.com/product-detail/MX17-Current-and-Volt...
Ignore the case and connector, on the basis that the circuit will be integrated into a larger scanner, and the cost will be substantially less. Most USB controllers already monitor current, so even the <$1 circuit probably would not be needed. The main cost would be the manufacturer putting together a database of power consumption figures to allow a pass/fail test.
Law enforcement, airports and so on already boxes to scan USB devices. They don't use them for every USB drive, just those that they decide they have cause to scan.
You're not going to get the uA level of detection to be able to decipher between a R/W operation and some sort of crypto in the CPU with these cheap components.