Final answer:
The currency reporting requirements under the Bank Secrecy Act necessitate travelers to declare amounts over $10,000 in currency or monetary instruments to U.S. Customs and Border Protection via FinCEN Form 105, known as the Currency and Monetary Instrument Report.
Step-by-step explanation:
The law that restricts the transport of more than $10,000 through an airport is related to the currency reporting requirements under the Bank Secrecy Act in the United States. When entering or leaving the U.S., or even transiting through, travelers must file a report with U.S. Customs and Border Protection if they are carrying more than $10,000 in currency or monetary instruments; this report is known as FinCEN Form 105 or the Currency and Monetary Instrument Report (CMIR). Failing to report the transportation of such amounts can result in the seizure of the currency and/or criminal penalties.
When discussing airport security measures post-September 11, the topic often refers to the comprehensive steps taken to prevent terrorist activities. These include installing reinforced cockpit doors, increasing the number of sky marshals on flights, and implementing sophisticated baggage scanners and face recognition technology at airports. In the context of this question, it's important to differentiate between security measures directly relating to anti-terrorism and regulations aiming to combat money laundering and other financial crimes.