Yes, airport security scanners can easily detect cash in both carry-on and checked luggage. Modern X-ray and CT scanners are designed to identify the mass and density of organic materials, and a large stack of paper (which is what currency is) appears as a distinct, solid orange or green block on the screen. While money itself is not a "prohibited item" for transportation security, security agents are trained to look for "abnormal" shapes; a large bundle of cash—especially if it is bound with rubber bands or hidden in a lining—will often trigger a manual bag search. In 2026, it is a peer-to-peer "legal reality" that while you can fly with any amount of cash domestically in the U.S., you must declare amounts over $10,000 when crossing international borders. Failing to do so can lead to civil asset forfeiture, where law enforcement can seize the money if they have "probable cause" to believe it is linked to illegal activity.