Urine and blood tests can usually only detect substances consumed in the past two to three days. A new technique, devised by Iritech in San Jose, CA, screens for longer-term drug use-up to two weeks-by looking at eye response. A person looks into a binocular-like camera and is exposed to a flash of light. Software calculates how quickly the pupils shrink and recover, compares this response against pupil records stored in a database, and gauges within seconds whether the subject has taken drugs or alcohol during the past several weeks.

Iritech CEO Daniel Daehoon Kim says the test would be best suited as a screening tool for prisons or for employers evaluating job applicants. One possible drawback: some legitimate medications, such as antiseizure drugs, affect pupil response and could cause false positives. The technology is 95 percent accurate, based on clinical studies involving more than 12,000 subjects. The company hopes to give the system its first real-world test this year at a prison in Santa Clara, CA.