A complete USB voltmeter/ammeter costs $1. https://www.alibaba.com/product-detail/MX17-Current-and-Voltage-Detector-USB_1601686055786.html https://www.alibaba.

A complete USB voltmeter/ammeter costs $1. https://www.alibaba.com/product-detail/MX17-Current-and-Voltage-Detector-USB_1601686055786.html 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.