The new methods use biometrics to analyze biochemical traces in sweat found along the ridges of a fingerprint. And those trace chemicals can quickly reveal whether you have ingested cocaine, opiates, marijuana, or other drugs. One novel, noninvasive forensic technique developed by researchers at the University of Surrey in the United Kingdom can detect cocaine and opiate use from a fingerprint in as little as 30 seconds. The team collected 160 fingerprint samples from 16 individuals at a drug-treatment center who had used cocaine within the past 24 hours—confirmed by saliva testing—along with 80 samples from non-users. The assay—which was so sensitive that it could still detect trace amounts of cocaine after subjects washed their hands with soap—correctly identified 99 percent of the users, and gave false positive results for just 2.5 percent of the nonusers, according to a paper published in Clinical Chemistry.

The researchers say they hope to expand the range of controlled substances that can be detected, which could include methamphetamines, amphetamines, and marijuana. The test can be modified to detect therapeutic drugs prescribed by physicians too.