I don't know if TSA uses a different ETD system than the rest of the world but the system used by TSA is plagued with false alarms. My definition of a false alarm is when the system alerts and no contraband is found. Perhaps this is caused by operator error, reusing test swabs, improper storage of test swabs, calibration, or detection thresholds settings. In my opinion when a test system of any kind alarms, no positive reason for that alarm is identified, then the testing system is suspect and near worthless.