Every year, billions of dollars hidden in clothing, baggage, and vehicles flow across the border into Mexico to pay for Americans’ drug habits. Now, chemists have devised a way to literally sniff out that smuggled cash. All U.S. bank notes emit a mixture of organic compounds that researchers have dubbed their “signature smell,” BBC reports. Human noses can’t pick up the odor, but the team hopes to develop a hand-held dollar detector that can. Such a device could be a great boon to border police, they said this week at the American Chemical Society meeting.